5 WAYS TO EXTEND MOLD LIFE: HEAT TREATMENT AND MATERIAL SELECTION STRATEGIES

5 WAYS TO EXTEND MOLD LIFE: HEAT TREATMENT AND MATERIAL SELECTION STRATEGIES

5 WAYS TO EXTEND MOLD LIFE: HEAT TREATMENT AND MATERIAL SELECTION STRATEGIES

The Key to Efficiency in Industrial Production

The fundamental requirement for staying competitive in the global manufacturing sector is to maximize quality standards while minimizing unit costs. In this equation, mold costs constitute a significant portion of the total production budget. The parameters determining a mold’s lifespan (die life) are complex; however, research shows that more than 70% of mold failures and shortened lifespans stem from incorrect material selection, faulty heat treatment, or inadequate design planning.

Mold life is not merely the wear rate of a metal; it is the holistic resistance that metal shows against thermal shocks, mechanical impacts, corrosion, and fatigue within its working environment. In this comprehensive guide, by combining our industrial experience as “Uyar Çelik” with metallurgical science, we will address step-by-step how you can multiply the life of your molds. This in-depth analysis, exceeding 2000 words, serves as a bedside resource that a manufacturing engineer should never be without.

1. Correct Material Selection and Metallurgical Quality

The mold manufacturing process is like a chain, and the weakest link in this chain is usually the raw material. The “death” (failure) of a mold is actually registered the moment the wrong material is selected during the design stage. When selecting a material, it is not enough to look only at the steel type (e.g., $1.2344$); the production method and the degree of purity of that steel are also of vital importance.

1.1. Analysis of Operating Conditions

Before selecting a material, the loads the mold will be exposed to must be correctly defined. If the mold operates at high temperatures (such as aluminum injection), “Hot Work Tool Steels” should be preferred. The most significant feature of these steels, “Hot Hardness,” ensures that the material maintains its strength even at temperatures like $600$°C. On the other hand, in cold cutting operations, impact strength and wear resistance take priority.

1.2. The Importance of ESR and VAR Technologies

Steels produced by traditional casting methods may contain microscopic impurities and gas voids. Steels produced using the ESR (Electroslag Remelting) method have a homogeneous structure purified from these impurities. This homogeneity ensures that the mold exhibits the same resistance at every point and reduces the risk of “warping” that may occur during heat treatment by 50%.

“The cheapest steel is not the one with the lowest purchase price; it is the steel that presses the most parts without error throughout the entire production process.”

2. Precision and Science in Heat Treatment

Heat treatment is a magical yet risky touch that turns a metal’s mechanical potential into reality. Many mold makers send steel for heat treatment just to “harden” it. However, the true purpose of heat treatment is to create a microstructure suitable for the operating conditions.

2.1. Austenitizing and Cooling Rate Control

When steel is heated to a certain temperature (Austenitizing temperature), its internal structure changes. The most critical point here is the soaking time at this temperature. If the duration is too short, the carbon does not dissolve, and the targeted hardness cannot be achieved. If it is kept too long, grain growth occurs, and the mold becomes incredibly brittle. In modern vacuum furnaces, these durations must be adjusted with second-level precision.

2.2. The Critical Role of Tempering

Steel emerging from the hardening process is practically a “ticking time bomb” due to the immense internal stress. The tempering process, performed to relieve this stress and provide toughness to the steel, is the most critical stage for mold life.

Especially in molds with complex geometries, the steel “breathes” slowly with each tempering step. Double tempering is standard, but triple tempering dramatically increases mold life. During this process, the furnace temperature calibration must not deviate by more than $+/-$ 5 degrees.

3. Design Strategies and Stress Concentration

Design flaws can cause even the most expensive steel to break during the first press. The most debated topic between metallurgical engineers and designers is sharp corners.

3.1. The Power of Radii Nature hates sharp corners, and so does steel. A sharp 90-degree corner in a mold can multiply the load placed upon it by 10 times. Every corner in the design should be given the largest possible radius (rounding). This ensures not only the absorption of impacts during operation but also the homogeneity of the cooling rate during heat treatment.

3.2. Thermal Management and Cooling Channels It is inevitable for a mold to heat up during operation. However, uncontrolled heating leads to spider-web-like cracks called “thermal fatigue” (Heat Checking). Cooling channels should be at a uniform distance from the mold surface and designed in a way that minimizes thermal shock.

5. Proactive Maintenance and Data Analysis

Maintenance is not about repairing when a problem occurs. Maintenance is about preventing the problem from occurring in the first place. Businesses that extend mold life subject the mold to a detailed inspection after every production run.

Stress Relief Annealing: When a mold reaches a certain number of cycles (for example, when it reaches 20% of its target life), it must be placed in a furnace at a low temperature (30-50 degrees below the tempering temperature). This process allows the metal to “rest” at an atomic level.

 
Maintenance StageWhen Is It Performed?Inspection / ProcessContribution to Mold Life
Post-Press Visual InspectionAfter every production runCracks, wear, burrs, deformation and surface defects are inspected.Minor damage is detected before it becomes serious.
Dimensional InspectionAt defined pressing intervalsDimensional loss, increased clearance and surface tolerances are checked in critical areas.A maintenance plan is created before part quality decreases.
Cleaning and LubricationAt the end of each shift or production runRemaining raw material, burrs, oxide and dirt on the surface are removed; proper lubrication is applied.Friction, sticking and surface fatigue are reduced.
Stress-Relief TemperingWhen approximately 20% of the target service life is reached or after intensive productionControlled heat treatment is applied at approximately 30–50°C below the tempering temperature.Internal stresses are reduced; the risk of cracking and early fatigue decreases.
Press Count TrackingContinuouslyFor each mold, press count, maintenance date, failure reason and process history are recorded.Maintenance is planned based on data, not estimates.

Frequently Asked Questions (FAQ)

Why high hardness (HRC) alone is not enough for mold life?

Hardness only measures wear resistance. However, molds are simultaneously exposed to impact and tensile loads. A mold that is too hard is brittle (Glass-like behavior). For mold life, a balance between “Toughness” and “Hardness” must be established.

Why does a mold crack during heat treatment?

It usually occurs due to an incorrect heating rate or excessively rapid cooling (Quenching). Steel changes volume as it heats and cools. If a corner cools and shrinks too quickly while the center is still hot and expanded, the steel cannot withstand its own internal tension and cracks.

How is "Heat Checking" (Thermal Cracking) delayed in hot work molds?

These cracks result from the thermal cycle. The solution involves subjecting the mold to a pre-heating process before operation and using steels with high thermal shock resistance and enhanced purity (ESR).

Is it always logical to make molds from stainless steel?

If you are using corrosive plastics (such as PVC) as raw material, yes. Otherwise, the machinability of stainless steels is more difficult and their cost is higher.

How should lubrication be performed to extend mold life?

Lubrication does not only reduce friction; it also creates a temporary thermal barrier on the mold surface. Automatic lubrication systems minimize human error, ensuring the mold always remains at an ideal level of lubricity.

What does the difference between HRC 60 and HRC 62 mean in practice?

The Rockwell hardness scale is a depth-based scale, not a linear one. Generally, it’s accepted that every 2-unit increase on the HRC scale approximately doubles the sharpness retention life. For example, a 52 HRC cutting tool might retain its sharpness for about a week, while a 62 HRC tool might stay sharp for much longer under similar conditions. This difference becomes particularly noticeable in industrial cutting tools.

Conclusion: The Era of Sustainable Productivity in Your Molds

Extending mold life isn’t just a process that begins with purchasing the right steel; it’s a combination of materials science, advanced engineering, and meticulous maintenance discipline. The material selection, heat treatment optimization, and design details we cover in this guide are the most concrete ways to reduce your production costs and increase your competitiveness in the market.

It should be remembered that the cheapest mold is not the one with the lowest initial cost, but the one that achieves the highest number of error-free prints throughout its lifespan. Incorrect heat treatment or the wrong steel choice can lead to downtime and financial losses that are difficult to recover from throughout the entire production chain.

At Uyar Çelik, we are not just a steel supplier, but a solution partner who stands by you at every stage of your projects. With our expert team, we aim to maximize the efficiency of your molds by providing the most accurate guidance at every step, from the metallurgical structure of the material to heat treatment protocols. For continuity and high performance in production, don’t compromise on quality materials and the right engineering approach.

Do you need steel bars in custom sizes?

Contact Uyar Çelik’s expert team. You can receive technical support and a price quote for our hot-rolled and cold-drawn steel bar varieties.

Phone: +90 (212) 485 9898

  Web: uyarcelik.com

Contact Us Now

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Ağırlık Hesaplama

Çelik profil ağırlığı — yuvarlak, lama, boru, kare, altıgen

Yuvarlak
Lama
Boru
Kare
Altıgen
mm
m
ad
Toplam Ağırlık
0
kg
Çap² × 0.006165 × Boy(m) × Adet
mm
mm
m
ad
Toplam Ağırlık
0
kg
Kalınlık × Genişlik × 0.00785 × Boy(m) × Adet
mm
mm
m
ad
Dış Çap²
0
İç Çap²
0
Fark
0
Toplam Ağırlık
0
kg
(Dış Çap² − İç Çap²) × 0.006165 × Boy(m) × Adet
mm
m
ad
Toplam Ağırlık
0
kg
Kenar² × 0.00785 × Boy(m) × Adet
mm
m
ad
Toplam Ağırlık
0
kg
s² × 0.0068 × Boy(m) × Adet
Çelik yoğunluğu: 7.85 g/cm³

Steel Weight Calculation Guide: Formulas for Round, Square, Flat, and Hexagonal Shapes

Steel Weight Calculation Guide: Formulas for Round, Square, Flat, and Hexagonal Shapes

The steel weight calculation guide covers an engineering process of critical importance across many fields, from the manufacturing industry to the construction sector. To determine the correct tonnage when placing an order, optimize shipping costs, arrive at accurate results in structural analyses, and efficiently plan your production process, you must accurately calculate the weight of steel materials.

In this guide, we provide a detailed overview of the weight calculation formulas, practical weight tables, and key considerations for calculating the weight of round, square, flat, and hexagonal steel bars included in Uyar Çelik’s product range.

1. The Basic Principle of Steel Weight Calculation

All steel weight calculations are based on a single fundamental physical principle:
Weight (kg) = Volume (cm³) × Density (g/cm³)
The standard density value for steel is accepted as 7.85 g/cm³ (7,850 kg/m³). This value applies to carbon steel and low-alloy steels. The density value may vary for high-alloy or special steels.
Therefore, the calculation of weight is based on three pieces of information:
The material’s geometric shape (round, square, flat bar, hexagonal)
Dimensions (diameter, side length, thickness, length)
Material density (g/cm³ or kg/m³)

Density Values of Different Types of Steel

Steel TypeDensity (g/cm³)Density (kg/m³)
Carbon Steel (S235, S355)7.857850
Quenched and Tempered Steel (42CrMo4, C45)7.857850
Free-Cutting Steel (11SMn30)7.857850
Stainless Steel (304)7.937930
Stainless Steel (316)7.987980
Tool Steel (1.2379 / D2)7.707700

2. Round Steel Bar Weight Calculation

Round steel bars are the most commonly used profile shape in industry. Hot-drawn round steel (EN 10060) has a wide range of applications, from shaft manufacturing to machine parts. At Uyar Çelik, we produce hot-drawn round steel in compliance with the EN 10060 standard.

Formula

Weight (kg/m) = d² × 0.006165

Here, d represents the diameter (mm).

The formula is derived as follows:

Weight (kg/m) = (π / 4) × d² × ρ / 1,000,000

Here, ρ = 7.85 g/cm³ and d is in mm. The constant factor 0.006165 is derived from (π/4) × 7.85 / 1000.

Example Calculation

The weight of a round steel bar with a diameter of 50 mm and a length of 6 meters:

Weight per meter = 50² × 0.006165 = 2,500 × 0.006165 = 15.41 kg/m
Total weight = 15.41 × 6 = 92.46 kg

Round Steel Bar Weight Chart (Weights per Meter)

Diameter (mm)kg/mDiameter (mm)kg/m
100.6176022.19
120.8886526.05
141.2087030.21
161.5787534.68
181.9988039.46
202.4668544.55
222.9849049.94
253.8539555.64
284.83410061.65
305.54911074.60
326.31312088.78
357.553130104.18
388.903140120.82
409.864150138.67
4210.878160157.76
4512.484170178.07
4814.205180199.61
5015.413200246.30

3. Square Steel Bar Weight Calculation

Square steel bars (EN 10059) are commonly used in machine manufacturing, steel construction, and the production of agricultural equipment. Uyar Çelik manufactures hot-drawn square steel bars in accordance with the EN 10059 standard.

Formula

Weight (kg/m) = a² × 0.00785

Here, a represents the side length (mm). The constant factor 0.00785 is equal to 7.85 / 1000.

Sample Calculation

40 × 40 mm square steel, 6 meters in length:

Weight per meter = 40² × 0.00785 = 1,600 × 0.00785 = 12.56 kg/m
Total weight = 12.56 × 6 = 75.36 kg

Square Steel Bar Weight Chart

Side (mm)kg/mSide (mm)kg/m
100.7855523.74
121.1306028.26
141.5396533.16
162.0107038.47
182.5437544.16
203.1408050.24
223.7988556.70
254.9069063.59
286.1549570.86
307.06510078.50
328.03811094.94
359.616120113.04
4012.560130132.67
4515.896140153.86
5019.625150176.63

4. Steel Bar (Flat Bar) Weight Calculation

Steel flat bars are flat steel bars with a rectangular cross-section (EN 10058). They are widely used in mold making, steel construction, machine manufacturing, agricultural tools and equipment, and the general metalworking industry. Uyar Çelik manufactures hot-rolled steel flat bars in accordance with the EN 10058 standard.

Formula

Weight (kg/m) = a × b × 0.00785

Here, a represents the width (mm) and b represents the thickness (mm).

Example Calculation

60 × 10 mm bar, 6 meters in length:

Weight per meter = 60 × 10 × 0.00785 = 4.71 kg/m
Total weight = 4.71 × 6 = 28.26 kg

5. Hexagonal Steel Bar Weight Calculation

Hexagonal steel bars (EN 10061) are particularly preferred for the production of bolts, nuts, hydraulic fittings, and automatic lathe work. Uyar Çelik manufactures hot-drawn hexagonal steel bars in accordance with the EN 10061 standard.

Formula

Weight (kg/m) = s² × 0.006798

Here, s represents the distance between opposing faces / keyway dimension (mm).

Derivation of the constant factor: 0.006798 = (3√3 / 2) × 7.85 / 1,000,000 × 10⁶. The formula for the hexagonal cross-sectional area is derived from (3√3/2) × s².

Sample Calculation

SW 32 mm hexagonal steel, 6 meters in length:

Weight per meter = 32² × 0.006798 = 1,024 × 0.006798 = 6.96 kg/m
Total weight = 6.96 × 6 = 41.76 kg

Hexagonal Steel Bar Weight Chart

SW (mm)kg/mSW (mm)kg/m
100,6804111,43
120,9794614,39
141,3325016,99
171,9645520,56
192,4536024,47
223,2906528,72
243,9147033,30
274,9557538,23
306,1188043,51
326,9578549,11
347,8579055,07
368,8099561,36
389,81210067,98

6. Summary Table of All Formulas

Profile ShapeFormula (kg/m)Constant FactorStandard
Roundd² × 0.0061650.006165EN 10060
Squarea² × 0.007850.00785EN 10059
Flata × b × 0.007850.00785EN 10058
Hexagonals² × 0.0067980.006798EN 10061

7. Key Considerations in Weight Calculation

Differences in Tolerance

The weight values given in the tables and formulas are theoretical (nominal) values. Actual weights may deviate from these values depending on manufacturing tolerances. According to EN standards, dimensional tolerances for steel bars generally range from ±1% to ±5%. These tolerances directly affect the weight.

The Impact of Steel Quality

A density of 7.85 g/cm³ can be used for standard structural steels (S235, S355) and high-strength steels (C45, 42CrMo4). However, since the density differs for high-alloy steels (stainless steel, tool steels), you must recalculate the constant factor in the formula using the material-specific density value.

Unit Conversions

The measurements in our formulas are in millimeters (mm). If you are working with different units, you can use the following conversion factors:

1 inch = 25.4 mm
1 cm = 10 mm
1 kg = 2.2046 lb
1 ton = 1,000 kg

The Difference Between Hot-Rolled and Cold-Drawn

The densities of hot-rolled and cold-drawn steels are practically the same; therefore, the same formulas are used. However, since dimensional tolerances are tighter in cold-drawn products, the difference between the theoretical and actual weights will be smaller.

Applications in Transportation and Logistics Planning

Accurate weight calculations for steel orders directly impact shipping costs. By taking into account the load capacity of trucks (typically 24–27 tons), adjusting the order quantity to align with the optimal shipment tonnage provides a cost advantage. At Uyar Çelik, we offer our customers the most efficient logistics planning from our facilities in Istanbul, Kocaeli, and Karabük.

8. The Importance of Accurate Weight Calculation in Industry

Accurate steel weight calculations directly impact many industrial processes:

Cost Estimation: Steel materials are typically priced per kilogram or ton. Calculating the weight accurately prevents errors in budget planning.
Structural Analysis: In engineering projects, the steel weight must be known to calculate the dead load of structural members.
Transportation Optimization: Without tonnage information, you cannot properly plan vehicle capacity. Incorrect calculations lead to underloading or overloading.
Production Planning: The weight of bars to be processed on CNC machines is necessary for calculating scrap rates and determining raw material requirements.
Crane and Lifting Capacity: Weight information is essential to ensure that the capacity of storage and handling equipment is not exceeded.

Frequently Asked Questions (FAQ)

Where does the number 0.00785 come from in steel weight calculations?

This constant is obtained by dividing the density of steel, 7.85 g/cm³, by 1000 (7.85 / 1000 = 0.00785). This conversion is necessary to convert measurements entered in millimeters to the kg/m unit.

Can I use the same formula for stainless steel?

No. The density of stainless steel varies (7.93 g/cm³ for grade 304 and 7.98 g/cm³ for grade 316). You need to recalculate the constant factor in the formula using the appropriate density value. For example, the square cross-section factor for 304 stainless steel would be 0.00793.

How much of a difference is there between the theoretical weight and the actual weight?

In production compliant with EN standards, the difference between theoretical and actual weight typically ranges from 1% to 5%. While this difference remains around 1–2% for cold-drawn products, the tolerance range is slightly wider for hot-rolled products.

When ordering steel bars, is weight or length more important?

Both are important. Orders are typically placed based on quantity and size, but pricing is calculated per kilogram or ton. Therefore, knowing both the quantity/size and the tonnage of your order is critical for budgeting and logistics.

Result: Steel Weight Calculation Guide: Formulas for Round, Square, Flat, and Hexagonal Shapes

Calculating the weight of steel is an extremely simple process once you know the correct formula. The weight formulas and tables for round, square, flat, and hexagonal steel bars shared in this guide provide values that you can use as a practical reference in your daily work.

As Uyar Çelik, with half a century of experience, we produce hot-rolled and cold-drawn steel in compliance with EN 10058, EN 10059, EN 10060, and EN 10061 standards. You can contact us for detailed information about our products manufactured at our facilities in Istanbul, Kocaeli, and Karabük, as well as for custom size requests.

Related Blog Posts:

Do you need steel bars in custom sizes?

Contact Uyar Çelik’s team of experts. You can receive technical support and a price quote for our range of hot-rolled and cold-drawn steel bars.

Phone: +90 (212) 485 9898 | Website: uyarcelik.com

www.uyarcelik.com

Contact Us Now

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Steel Selection in the Automotive Supplier Industry: A Material Guide in Compliance with OEM Standards

Steel Selection in the Automotive Supplier Industry: A Material Guide in Compliance with OEM Standards

Steel Selection in the Automotive Supplier Industry: A Material Guide in Compliance with OEM Standards

The automotive industry is one of the largest consumers of steel worldwide. On average, approximately 55% of a passenger vehicle’s weight consists of steel and iron alloys. Considering that this ratio can reach up to 65% in commercial vehicles, the critical importance of steel selection becomes clear.

However, using just any type of steel is not sufficient in automotive component manufacturing. OEM (Original Equipment Manufacturer) companies expect their suppliers to provide materials that comply with specific standards, tolerances, and certifications. Incorrect steel selection can lead to production defects, high scrap rates, warranty return costs, and most importantly, serious safety risks.

In this guide, we thoroughly examine steel selection in the automotive supplier industry, including OEM standard requirements, recommended steel grades for different vehicle components, and the critical factors you should consider during your procurement process.

 

1. Why Is Steel So Important in the Automotive Industry?

It is one of the industries with the highest expectations from steel. In modern vehicles, steel is used as a load-bearing element in the chassis and body structure, to provide high strength and wear resistance in engine and transmission components, in applications requiring fatigue strength such as suspension and steering systems, and for impact absorption in safety components.

Each application area requires different mechanical properties, surface qualities, and machinability characteristics. For example, while high yield strength and good weldability are essential for a chassis cross member, hardness, wear resistance, and tight tolerances are critical for a gear shaft.

In recent years, with the lightweighting trend, the use of high-strength steels (AHSS – Advanced High Strength Steel) has been increasing rapidly. These steels provide the same load-bearing capacity with thinner sections, contributing to reduced vehicle weight and improved fuel efficiency.

2. OEM Standards and Quality Requirements

The fundamental standards and requirements that every supplier working with automotive OEM companies must know are as follows:

2.1. IATF 16949 Quality Management System

IATF 16949 is the global quality management system standard for the automotive industry. Previously known as ISO/TS 16949, this standard builds on ISO 9001 and extends it with requirements specific to the automotive sector. From the perspective of steel suppliers, IATF 16949 includes strict rules on material traceability (from casting to the final product), process capability (Cpk values), PPAP (Production Part Approval Process) documentation, and corrective and preventive action processes.

2.2. VDA Standards (German Automotive Industry)

German OEMs such as Volkswagen, BMW, Mercedes-Benz, and Audi expect their suppliers to comply with VDA 6.3 process audit and VDA 6.5 product audit standards.

In terms of steel materials, VDA standards include detailed requirements particularly regarding the format of material test reports, sampling methods, and surface quality criteria. Considering that Türkiye is one of the largest automotive exporters to Europe, compliance with VDA standards is especially critical.

2.3. OEM Material Specifications

Each major OEM company has its own material specifications. These specifications generally refer to EN or SAE standards, but also include additional requirements:

Volkswagen: VW 50065 (cold-forming steels), TL 4225 (steel tubing)
Ford: WSS-M1A365 (high-strength steels), FLTM-BI series (mechanical tests)
Toyota: TSH series (Toyota Steel Specifications)
General Motors: GMW series (Global Material & Welding Standards)

3. Steel Grade Guide by Vehicle Components

 
Application AreaRecommended Steel GradeKey PropertyStandard Reference
Chassis and structural componentsS355MC, S420MC, S460MCHigh yield strength, good weldabilityEN 10149-2
Gears and shaft components16MnCr5, 20MnCr5, 42CrMo4Case hardening or quenched & tempered steel, high wear resistanceEN 10084, EN 10083
Suspension components38MnB5, 33MnCrB5-2High fatigue strength, resistance to impact loadsEN 10083-3
Engine componentsC45, C45E, 42CrMo4Quenched & tempered steel, high temperature resistanceEN 10083-2
Fasteners (bolts, nuts)23MnB4, 32CrB4Suitable for cold forming, high tensile strengthEN 10263
Exhaust system1.4509, 1.4512 (stainless)High temperature and corrosion resistanceEN 10088
Sheet metal body componentsDC04, DC06, HX340LADDeep drawability, high surface qualityEN 10130, EN 10268

3.1. Chassis and Structural Steels

The chassis is the structural framework that carries all the loads of a vehicle. Therefore, chassis steels must provide high yield strength (minimum 355–460 MPa), excellent weldability, suitability for cold forming, and consistent mechanical properties.

Grades such as S355MC, S420MC, and S460MC are widely used in the production of critical structural components like cross members, control arms, and chassis extensions. These steels are produced using the thermomechanical controlled processing (TMCP) method, and their alloying element content is kept low to maintain good weldability.

3.2. Gears, Shafts, and Transmission Components

Transmission components represent one of the most critical segments of steel consumption in the automotive industry. Gears and shafts operate under high torque and must resist wear over millions of cycles.

Two main steel categories stand out for these applications:

Case hardening steels (16MnCr5, 20MnCr5): Ideal for parts requiring a hard outer surface and a tough core. After the carburizing process, surface hardness reaches 58–62 HRC while core toughness is maintained.

Quenched and tempered steels (42CrMo4): Preferred for components that require homogeneous mechanical properties throughout the entire cross-section. Crankshafts, axle shafts, and high-strength bolts are typical applications in this group.

Important note: Dimensional tolerances are extremely critical for transmission steels. Cold drawn round steel bars offer tighter tolerances compared to hot rolled steels, reducing machining effort before processing and minimizing scrap rates.

Practical Effects of Chemical Composition

The higher carbon and manganese content of S355 provides it with superior mechanical strength. However, this creates a trade-off:

Higher carbon = Higher strength + Lower weldability
Lower carbon = Lower strength + Better weldability

Carbon equivalent (CEV) is the most reliable indicator of weldability. As the CEV value increases, the need for preheating during welding also increases, and the risk of cold cracking rises. The low CEV value of S235 (≤0.35) makes it an ideal steel for welding without preheating. For S355, however, preheating may be required in thicker sections (typically >25 mm).

3.3. Suspension and Steering System

Suspension components are subjected to millions of repeated load cycles throughout the vehicle’s lifetime. Therefore, fatigue strength is the most critical parameter in steel selection.

Boron-alloyed steels such as 38MnB5 and 33MnCrB5-2 are commonly preferred for parts like stabilizer bars, tie rod ends, control arms, and torsion springs. Boron, even when added in very small amounts (typically in the range of 0.001–0.003), significantly increases hardenability and enables the material to achieve high strength levels after heat treatment.

3.4. Fasteners (Steel Bolts and Nuts)

Automotive fasteners may appear simple, but they are extremely critical safety components. The failure of a wheel bolt, for example, can pose a direct life-threatening risk. For this reason, automotive bolts are typically manufactured in strength classes such as 8.8, 10.9, or 12.9.

Steels suitable for cold forging (such as 23MnB4 and 32CrB4) enable high production speeds and low scrap rates. Material certificates (EN 10204 Type 3.1) must include complete information on chemical composition, mechanical test results, and heat treatment parameters.

4. Hot Rolled vs. Cold Drawn Steel: Which One to Use in Automotive Applications?

 
CriteriaHot RolledCold Drawn
Dimensional toleranceWide tolerance (EN 10058–10061)Tight tolerance (h9–h11)
Surface qualityScaled, rough surfaceSmooth, bright surface
Automotive usageChassis, structural parts, welded componentsShafts, pins, hydraulic pistons, CNC parts
CostLower unit costHigher unit cost, but lower total processing cost
MachiningRequires more material removalLess material removal, faster processing

Practical recommendation: When you choose cold drawn steel for automotive parts produced through CNC machining, the raw material cost may be higher, but the total part cost is usually lower. This is due to reduced material removal, shorter machining time, and lower scrap rates.

5. Material Certification and Traceability

OEM companies require full traceability of every material in the supply chain. Material certificates prepared according to the EN 10204 standard are essential documents in steel procurement.
Certificate TypeDescriptionUse in Automotive
Type 2.2Manufacturer’s declarationGenerally not accepted
Type 3.1Test report verified by independent inspectionStandard requirement
Type 3.2Verified by manufacturer and purchaser representativeRequired for safety-critical parts

The information that must be included in a Type 3.1 certificate are: the heat number, chemical analysis results, mechanical test results (tensile strength, yield strength, elongation, hardness), dimensional measurements, heat treatment conditions (if applicable), and surface inspection results. Heat number traceability is critically important in the automotive industry, especially in recall situations.

6. Common Mistakes in Steel Selection

  • Focusing only on price: Low-cost steel may lead to high scrap rates and rejected batches in production due to inconsistent chemical composition and mechanical properties.

  • Selecting the wrong steel grade: For example, using quenched and tempered steel where case hardening steel is required, or vice versa.

  • Ignoring tolerance class: Hot rolled steel with wide tolerances can result in additional operations and increased costs in applications requiring precise CNC machining.

  • Lack of certification: Producing with materials without a Type 3.1 certificate can lead to serious non-conformities during OEM audits.

  • Neglecting supplier diversity: Single-source supply increases supply security risks. OEM companies typically require at least two approved suppliers.

7. Evaluation Criteria for Supplier Selection

As an OEM-approved automotive component manufacturer, it is recommended to evaluate the following criteria when selecting your steel supplier:

  • Product range diversity: The ability to source hot rolled, cold drawn, and engineering steels from a single supplier provides logistical advantages.

  • Stock capacity and delivery speed: Downtime in automotive production lines is extremely costly. The supplier’s ability to deliver quickly from multiple locations is critical.

  • Quality certifications: Full compliance with ISO 9001, IATF 16949, and the ability to provide EN 10204 Type 3.1 certificates.

  • Technical consultancy: A team with industry experience that can provide engineering support in selecting the correct steel grade.

  • Global sourcing capability: A supplier structure that can source steel from international markets while maintaining the same level of quality assurance for imported products.

8. Future Trends in Automotive Steel

The automotive industry is undergoing significant transformations in steel usage, especially with the rise of the electric vehicle (EV) revolution. The key trends expected to shape the future are:

  • Increasing share of high-strength steels (AHSS): In line with lightweighting goals, 3rd generation AHSS steels (combining excellent ductility and high strength) will become more widespread.

  • Special steel requirements for electric vehicles: Steels with high energy absorption capacity will be in demand for battery enclosures and protective structures.

  • Growing demand for green steel: With the European CBAM regulation, low carbon footprint steel supply will become a decisive factor in OEM selection criteria.

  • Digital traceability: Blockchain-based material traceability systems will enhance transparency across the supply chain.

9. Conclusion: Steel Selection in the Automotive Supplier Industry

Selection is not only a technical decision; it is also a strategic one that directly affects cost, quality, supply security, and customer satisfaction. Supplying materials in compliance with OEM standards forms the foundation of long-term business partnerships.

To ensure the correct steel selection, follow these steps: first, clearly define the mechanical requirements of the application; then refer to the relevant EN, SAE, or OEM specification; conduct a total cost analysis between hot rolled and cold drawn alternatives; verify the completeness of material certifications; and evaluate your supplier’s supply reliability and logistics capabilities.

As Uyar Steel, we offer a wide product range in hot rolled, cold drawn, and engineering steel products.
With fast delivery from our locations in Istanbul, Karabük, Kocaeli, and Düsseldorf, Type 3.1 material certificates, and technical consultancy services, we are here to support you.
For detailed information and quotations: www.uyarcelik.com/contact

In addition to cross-sectional tolerances, the length tolerance, straightness values, and surface quality of steel bars are also key parameters that directly affect the production process. Standard length tolerances for hot-rolled bars are generally applied as +50 mm / 0 mm (positive deviation). For cold-drawn bars, tighter standard length tolerances such as ±5 mm are commonly offered. From suppliers that provide precision cutting services, cutting tolerances of ±1–2 mm can be requested, which can significantly reduce CNC preparation time.

Straightness (bar bow) is particularly critical in the CNC machining of long parts and in the production of hydraulic piston rods. In hot-rolled bars, straightness values are typically in the range of 3–5 mm/m. In cold-drawn bars, straightness of 0.5–1.0 mm/m can be achieved. In straightened bars, this value can be reduced to below 0.3 mm/m. In hydraulic piston rod applications, the straightness value should not exceed 0.5 mm/m; otherwise, seal life and sealing performance may be negatively affected.

In terms of surface quality, hot-rolled bars have a surface covered with mill scale, and their surface roughness (Ra) is generally in the range of 6.3–12.5 micrometers. In cold-drawn bars, surface roughness decreases to 0.8–3.2 micrometers. In ground and polished bars, values of 0.2–0.4 micrometers can be achieved. For parts that will undergo chrome plating, painting, or other surface treatments, the quality of the base surface directly affects coating adhesion and final appearance.

10. Frequently Asked Questions (FAQ)

Which steel grades are most commonly used in the automotive industry?

Steel grades used in the automotive industry vary depending on the application. High-strength structural steels such as S355MC and S420MC are used in chassis and load-bearing structures; 16MnCr5 and 20MnCr5 (case hardening steels) and 42CrMo4 (quenched and tempered steel) are used in gear and shaft production; and grades suitable for cold forging such as 23MnB4 and 32CrB4 are preferred for fasteners. It is important to refer to OEM specifications for the correct selection.

Is the IATF 16949 certification mandatory for steel suppliers?

IATF 16949 is the global quality management system standard expected by automotive OEM companies from their suppliers. It is generally mandatory for Tier 1 suppliers that directly supply parts to OEMs. For raw material suppliers, ISO 9001 may be sufficient; however, compliance with IATF 16949 provides a competitive advantage. From the perspective of steel suppliers, the most critical requirement is the ability to ensure material traceability and provide EN 10204 Type 3.1 certification.

Which should be preferred for automotive applications: hot rolled or cold drawn steel?

Both types of steel have their place in automotive applications. Hot rolled steels offer a cost advantage in structural parts such as chassis cross members and components requiring welding. Cold drawn steels, on the other hand, reduce total production cost in parts manufactured by CNC machining, such as shafts, pins, and components requiring tight tolerances. As a general rule, focusing on total part cost rather than raw material unit price is the most accurate approach.

How do electric vehicles affect steel demand?

It shows that while transmission components are becoming simpler, demand is increasing for steels with high energy absorption capacity used in battery enclosures and protective structures. Additionally, due to the weight sensitivity of EVs, the use of 3rd generation AHSS (Advanced High Strength Steel) is becoming more widespread. It is observed that the total steel usage per vehicle has not decreased, but the types of steel used are changing.

What information should be included in a steel material certificate (Type 3.1)?

The EN 10204 Type 3.1 certificate must include the following information: heat number, chemical analysis results (C, Mn, Si, Cr, Mo, Ni, etc.), mechanical test results (tensile strength, yield strength, elongation percentage, hardness), dimensional measurements, heat treatment conditions, and surface inspection results.

This document must be verified by an independent inspection body. Heat number traceability is critically important in the event of a potential product recall.

Selecting steel in compliance with OEM standards is a critical step for ensuring production quality and long-lasting performance. Contact Uyar Çelik to determine the most suitable steel grade for your project and receive technical support.

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Steel Bar Size and Tolerance Table: A Comprehensive Guide According to EN Standards

Steel Bar Size and Tolerance Table: A Comprehensive Guide According to EN Standards

Steel bar dimensional tolerances and measurement tables are critical parameters that directly affect production efficiency and final part quality. Engineers and procurement professionals often need to compare tolerance values across different EN standards and select the most suitable bar form for their projects.

Tolerance selection has a direct impact on CNC machining costs, material waste, and the precision of the final component. Using a bar with wide tolerances for a high-precision part leads to additional material removal and increased tool wear, while selecting unnecessarily tight tolerances results in higher raw material costs.

In this guide, we present the applicable EN standards for hot-rolled and cold-drawn steel bars, tolerance tables, dimensional ranges based on profile types, and practical recommendations for selecting the right tolerance.

1. EN Standards: Which Standard Covers Which Profile?

Standardized according to European Norms (EN). A separate EN standard applies to each profile form:

EN StandardProfile TypeDescriptionSize Range
EN 10060RoundHot-rolled round steel barØ10–280 mm
EN 10059SquareHot-rolled square steel bar10×10–200×200 mm
EN 10058Flat (Strip)Hot-rolled flat steel bar10×6–120×60 mm
EN 10061HexagonalHot-rolled hexagonal steel barAF 14.5–100 mm
EN 10278All profilesCold-drawn (bright) steel barVaries depending on profile type

2. EN 10060: Hot-Rolled Round Steel Tolerances

Nominal Diameter (mm)Tolerance (mm)Ovality Tolerance (mm)
10–25±0.475% of diameter tolerance
25–50±0.4 – ±0.575% of diameter tolerance
50–100±0.5 – ±0.875% of diameter tolerance
100–150±0.8 – ±1.075% of diameter tolerance
150–250±1.0 – ±1.675% of diameter tolerance
250–280±1.6 – ±2.075% of diameter tolerance

Example: A hot-rolled round bar with a nominal diameter of 50 mm may have an actual diameter between 49.5–50.5 mm according to EN 10060. If precision parts will be machined using CNC, sufficient machining allowance should be considered based on this tolerance range.

3. EN 10059: Hot-Rolled Square Steel Tolerances

Side Length (mm)Tolerance (mm)Corner Radius (max)Out-of-Square Tolerance
10–25±0.412% of side length75% of side tolerance
25–50±0.4 – ±0.512% of side length75% of side tolerance
50–100±0.5 – ±0.810% of side length75% of side tolerance
100–200±0.8 – ±1.38% of side length75% of side tolerance

4. EN 10058: Hot-Rolled Flat Steel Tolerances

Flat bars require two-dimensional tolerances: width and thickness. EN 10058 defines separate tolerance values for these two parameters.

Width tolerances:
For widths of 10–50 mm: ±0.5 – ±0.8 mm
For widths of 50–100 mm: ±0.8 – ±1.5 mm
For widths of 100–120 mm: ±1.5 – ±2.0 mm

Thickness tolerances:
For thicknesses of 5–10 mm: ±0.3 – ±0.4 mm
For thicknesses of 10–25 mm: ±0.4 – ±0.5 mm
For thicknesses of 25–60 mm: ±0.5 – ±0.8 mm

The edge profile of flat steel bars is also important. EN 10058 offers both standard (rounded edge) and sharp edge options. For flat bars that will be machined by CNC, choosing sharp edges provides advantages in terms of clamping and alignment.

5. EN 10061: Hot-Rolled Hexagonal Steel Tolerances

Hexagonal bars are toleranced based on the across flats dimension (AF – Across Flats).
AF Dimension (mm)Tolerance (mm)Out-of-Square Tolerance
14.5–25±0.3 – ±0.475% of AF tolerance
25–50±0.4 – ±0.575% of AF tolerance
50–100±0.5 – ±0.875% of AF tolerance

Hexagonal bars are widely used in the production of bolts and nuts, valve bodies, and fastening elements that require wrench engagement. Cold-drawn hexagonal bars offer significantly tighter tolerances (h9–h11) compared to hot-rolled alternatives and are ready for direct machining on CNC automatic lathes.

6. EN 10278: Cold-Drawn (Bright) Steel Tolerances

Nominal Size (mm)h9 Tolerance (µm)h10 Tolerance (µm)h11 Tolerance (µm)
6–100 / –360 / –580 / –90
10–180 / –430 / –700 / –110
18–300 / –520 / –840 / –130
30–500 / –620 / –1000 / –160
50–800 / –740 / –1200 / –190
80–1200 / –870 / –1400 / –220

Note: h tolerance classes represent unilateral (negative) deviation: the nominal size is the upper limit, and the actual size is always below the nominal value. For example, a Ø50 mm cold-drawn round bar with h9 tolerance is delivered within the range of 49.938–50.000 mm.

7. Hot-Rolled vs Cold-Drawn: Tolerance Comparison

ParameterHot-Rolled (EN 10060)Cold-Drawn (EN 10278, h9)
Tolerance Band±0.5 mm (±500 µm)0 / –62 µm
Total Tolerance Range1.0 mm0.062 mm
Ratio—~16 times more precise
Surface Roughness (Ra)6.3–12.5 µm0.8–3.2 µm

This comparison clearly demonstrates why cold-drawn bars are preferred in CNC machining. A tolerance that is 16 times more precise means less material removal, shorter machining time, and lower scrap rates.

8. Practical Recommendations for Selecting the Right Tolerance

For CNC machining: use cold-drawn bars with h9 or h11 tolerances. By keeping machining allowance to a minimum, you can reduce processing time and tool wear.

For forging and hot forming: hot-rolled bars with wider tolerances are usually sufficient. Since the material will already be reshaped at high temperature, precise tolerances are generally unnecessary.

For welded structures: hot-rolled bars are typically adequate, as the final dimensions can be achieved through post-weld machining.

For hydraulic piston rods: cold-drawn, ground, and polished bars are required. An h8 tolerance and a surface finish of Ra 0.2–0.4 µm are generally targeted.

For automatic lathes: cold-drawn bars with h11 tolerance are ideal for serial production. They provide the dimensional consistency needed for automatic feeding systems.

For dimensional verification: inspect received bars by taking sample measurements with calipers or micrometers to confirm tolerance compliance. Use the dimensional data in the EN 10204 Type 3.1 certificate as a reference.

8.5. Length Tolerance, Straightness, and Surface Quality

In addition to cross-sectional tolerances, the length tolerance, straightness values, and surface quality of steel bars are also key parameters that directly affect the production process. Standard length tolerances for hot-rolled bars are generally applied as +50 mm / 0 mm (positive deviation). For cold-drawn bars, tighter standard length tolerances such as ±5 mm are commonly offered. From suppliers that provide precision cutting services, cutting tolerances of ±1–2 mm can be requested, which can significantly reduce CNC preparation time.

Straightness (bar bow) is particularly critical in the CNC machining of long parts and in the production of hydraulic piston rods. In hot-rolled bars, straightness values are typically in the range of 3–5 mm/m. In cold-drawn bars, straightness of 0.5–1.0 mm/m can be achieved. In straightened bars, this value can be reduced to below 0.3 mm/m. In hydraulic piston rod applications, the straightness value should not exceed 0.5 mm/m; otherwise, seal life and sealing performance may be negatively affected.

In terms of surface quality, hot-rolled bars have a surface covered with mill scale, and their surface roughness (Ra) is generally in the range of 6.3–12.5 micrometers. In cold-drawn bars, surface roughness decreases to 0.8–3.2 micrometers. In ground and polished bars, values of 0.2–0.4 micrometers can be achieved. For parts that will undergo chrome plating, painting, or other surface treatments, the quality of the base surface directly affects coating adhesion and final appearance.

8.6. Cost Impact of Tolerance Selection

Tolerance selection directly affects the total part cost. Although cold-drawn bars with tighter tolerances have a higher unit price, they generally reduce overall cost by shortening CNC machining time and minimizing material waste. For example, in the production of a 50 mm diameter shaft, using a hot-rolled bar may require approximately 1 mm of material removal, whereas with an h9 tolerance cold-drawn bar, this value decreases to 0.062 mm. This difference can reduce CNC machining time by approximately 40–60%.

Additionally, selecting the appropriate tolerance class helps prevent unnecessary costs caused by purchasing overly precise bars. For instance, choosing an h9 tolerance for a bar used in forging or welded structures does not provide any technical advantage but increases cost. As a general principle, selecting the widest tolerance that meets the final machining requirements and part precision ensures an optimal cost-performance balance.

8.7. Tolerance Verification in the Procurement Process

Performing dimensional verification upon receiving your products is essential for quality assurance. It is recommended to take measurements from the beginning, middle, and end sections of the bar using a caliper or micrometer. For ovality control in round bars, measurements should be taken in two perpendicular directions at the same cross-section.

The EN 10204 Type 3.1 certificate indicates that the supplier has independently verified the dimensional data and is a mandatory document, especially in the automotive, defense, and hydraulic sectors. Ensuring that your supplier maintains stock in different tolerance classes (e.g., EN 10060 standard, EN 10278 h9/h11) and can provide a Type 3.1 certificate offers assurance for production continuity.

8. Future Trends in Automotive Steel

  • Increasing share of high-strength steels (AHSS): In line with lightweighting goals, 3rd generation AHSS steels (excellent ductility + high strength) will become more widespread.

  • Special steel requirements for electric vehicles: Steels with high energy absorption capacity will be required for battery enclosures and protective structures.

  • Demand for green steel: With the European CBAM regulation, low carbon footprint steel supply will become a key selection criterion for OEMs.

  • Digital traceability: Blockchain-based material traceability systems will increase transparency in the supply chain.

Frequently Asked Questions (FAQ)

What is the difference between h9 and h11 tolerances?

h9 has a tighter (more precise) tolerance range than h11. For example, at a Ø50 mm diameter, h9 tolerance is –62 µm, while h11 tolerance is –160 µm. h9 is more expensive but allows less material removal in CNC machining. The selection depends on the required precision of the final part.

Can hot-rolled bars be machined with CNC?

Yes, hot-rolled bars can be machined with CNC. However, due to their wide tolerances, more material removal is required; the scaled surface accelerates tool wear, and dimensional inconsistencies increase machining time. In serial CNC production, cold-drawn bars generally reduce the total part cost.

Which profiles are covered by the EN 10278 standard?

EN 10278 covers all profiles of cold-drawn (bright) bars: round, square, hexagonal, and flat. It replaces the former DIN standards DIN 668 (round), DIN 670 (square), and DIN 671 (hexagonal).

International Standard Equivalents

Knowing the international equivalents of EN standards is especially important in export projects. The former DIN equivalents are as follows: EN 10060 (round) corresponds to DIN 1013, EN 10059 (square) corresponds to DIN 1014, EN 10058 (flat) corresponds to DIN 1017, and EN 10061 (hexagonal) corresponds to DIN 1015. For cold-drawn steels, EN 10278 replaces the former DIN standards DIN 668 (round), DIN 670 (square), and DIN 671 (hexagonal).

In terms of American standards, ASTM A29/A29M (hot-rolled round and square) and ASTM A108 (cold-drawn) are the main reference standards. Since the ASTM tolerance system differs from EN, both standards may need to be compared in international projects. In Türkiye, the TS EN equivalents of EN standards are valid and published by TSE.

The products in Uyar Çelik’s range—including hot-rolled flat steel (EN 10058), hot-rolled square (EN 10059), hot-rolled round steel (EN 10060), and hot-rolled hexagonal (EN 10061)—are manufactured and delivered in full compliance with these EN standards. Cold-drawn bars are offered in accordance with EN 10278 in h9–h11 tolerance classes.

Conclusion: Steel Bar Dimensions and Tolerance Table

It forms the foundation of correct material procurement and efficient production. EN 10060, EN 10059, EN 10058, EN 10061, and EN 10278 standards define clear tolerance values for hot-rolled and cold-drawn bars.

Selecting the right tolerance prevents unnecessary cost increases and improves production efficiency. In CNC machining applications, the tighter tolerances of cold-drawn bars stand out, while in forging and welding applications, the cost advantage of hot-rolled bars becomes more prominent.

By saving this guide as a reference, you can quickly determine the appropriate standard and tolerance class for your future steel bar orders.

As Uyar Çelik, we maintain a wide stock range of EN-compliant hot-rolled and cold-drawn steel bars (round, square, flat, and hexagonal).

For the supply of Type 3.1 certified, dimensionally guaranteed bars:


www.uyarcelik.com/iletisim

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S235 (St37) vs S355 (St52) Steel Comparison: Differences, Properties, and the Right Choice

S235 (St37) vs S355 (St52) Steel Comparison: Differences, Properties, and the Right Choice

S235 (St37) vs S355 (St52) Steel Comparison: Differences, Properties, and the Right Choice

Structural steel selection is a critical engineering decision that directly affects the safety, cost, and lifespan of a project. S235 (formerly St37) and S355 (formerly St52), the two most commonly used structural steel grades in Turkey and worldwide, have different mechanical properties, chemical compositions, and application areas. Incorrect steel selection can lead to unnecessary cost increases or, worse, structural safety risks.

In this guide, drawing on Uyar Çelik’s half-century of experience, we explain the differences, properties, and the right choice for each project with clear examples of S235 (St37) vs S355 (St52) steel comparison.

1. Standardization System: Transition from DIN to EN

In Turkey, the steel designations St37 and St52, still widely used, belong to the old DIN standard classification originating from Germany. Today, the EN 10025 standard, valid throughout the European Union, has replaced these designations. However, the old designations are still frequently used in the field, workshops, and ordering processes.

In the S235 and S355 designations, the “S” stands for “Structural,” while the number next to it indicates the minimum yield strength of that steel in MPa (Megapascals). Thus, the minimum yield strength of S235 is 235 MPa, and that of S355 is 355 MPa.

Standard Equivalent Table

EN 10025DINTS (Former)ASTM Equivalent
S235JRSt37-2Fe 37A36
S235J0St37-3UFe 37A36
S235J2St37-3NFe 37A36
S355JRSt52-3UFe 52A572 Gr.50
S355J0St52-3UFe 52A572 Gr.50
S355J2St52-3NFe 52A572 Gr.50
S355K2St52-3NFe 52A572 Gr.50

2. Comparison of Mechanical Properties

Mechanical properties are the most decisive factor in steel selection. The following table compares the basic mechanical properties of S235 and S355 steels:
Mechanical PropertyS235 (St37)S355 (St52)
Minimum Yield Strength235 MPa355 MPa
Tensile Strength360–510 MPa470–630 MPa
Minimum Elongation at Break (≥16 mm)%26%22
Brinell Hardness (HB)100–154150–210
Modulus of Elasticity210 GPa210 GPa
Density7.85 g/cm³7.85 g/cm³

What do these numbers mean?

  • Yield strength is the maximum stress a steel can withstand before undergoing permanent deformation. S355 has approximately 51% higher yield strength than S235. This means you can use thinner sections of S355 to carry the same load, reducing overall structural weight and material costs.
  • Tensile strength is the stress a material can withstand until it reaches fracture. S355 offers significantly higher tensile strength compared to S235, a property that is particularly critical in structures under dynamic loads.
  • Fracture elongation indicates how much a steel can stretch before fracturing. S235 has an advantage in this area; it possesses higher ductility. This facilitates forming and bending processes.

3. Comparison of Chemical Compositions

Chemical composition is the primary factor determining the mechanical properties, weldability, and corrosion resistance of steel.
ElementS235 (max. %)S355 (max. %)
Carbon (C)0.17–0.200.20–0.23
Manganese (Mn)1.401.60
Silicon (Si)0.0350.55
Phosphorus (P)0.0350.035
Sulfur (S)0.0350.035
Nitrogen + Sulfur0.0120.012
Carbon Equivalent (CEV)≤0.35≤0.47

Practical Effects of Chemical Composition

S355’s higher carbon and manganese content gives it superior mechanical strength. However, this creates a trade-off:

High carbon = High strength + Lower weldability
Low carbon = Lower strength + Better weldability

Carbon equivalent (CEV) is the most reliable indicator of weldability. As the CEV value increases, the need for preheating during welding increases, and the risk of cold cracking rises. S235’s low CEV value (≤0.35) makes it an ideal steel that can be welded without preheating. For S355, however, preheating may be required for thick sections (usually >25 mm).

4. Comparison of Resource Capabilities

Welding is the most common joining method in steel structures and is a parameter that must be considered when selecting steel.
Welding ParameterS235 (St37)S355 (St52)
WeldabilityExcellentGood
Preheating RequirementGenerally not requiredRequired for thick sections
Cold Cracking RiskLowMedium
Recommended Welding MethodMIG/MAG, ElectrodeMIG/MAG, TIG, Submerged Arc
Post-Weld Heat TreatmentRarely requiredRecommended for thick sections

Practical advice: If your project involves intensive welding and involves working with thick sections, the S235 offers an easier and more economical solution. However, welding can also be done without problems with the S355 using low-hydrogen electrodes and proper preheating.

5. Applications: Which Steel Should Be Preferred Where?

5.1. Applications Where S235 (St37) Should Be Preferred

Light steel construction structures (warehouses, hangars, roof supports)
General purpose pipe and profile manufacturing
Low and medium load bearing structural elements
Agricultural machinery and equipment
Stair, railing and platform structures
Parts requiring intensive bending and shaping
Projects where budget is a priority

5.2. S355 (St52) Preferred Applications

Heavy steel structures (bridges, viaducts, high-rise buildings)Crane and lifting equipment chassis
Pressure vessels and pipelines
Shipbuilding and marine structures
Wind turbine towers
Heavy construction machinery chassis and platforms
All types of structures requiring high load-carrying capacity
Projects requiring weight optimization (same strength with thinner sections)

6. Cost and Economic Evaluation

When selecting steel, looking solely at the price per kg can be misleading. A proper comparison requires evaluating the total project cost.

Unit Price Comparison

S355 is approximately 5–15% more expensive per kg compared to S235. However, it is not accurate to evaluate this difference solely based on unit price.

Savings Through Cross-Section Optimization

Thanks to the high yield strength of S355, thinner and lighter sections can be used to carry the same load. This results in:

  • Reduced total steel consumption (saving tons, especially in large projects)
  • Lower transportation costs (less tonnage = fewer vehicles)
  • Reduced foundation load (lighter structure = more economical foundation)
  • Shorter assembly time (less material = faster workmanship)

Example scenario: Where you need to use S235 steel with 200×10 mm flat bars on an industrial roof, you can achieve the same load-bearing capacity using S355 steel with 200×8 mm flat bars. This translates to approximately 20% less steel consumption per meter and a significant reduction in associated costs.

7. Formability and Machinability

ProcessS235 (St37)S355 (St52)
Cold BendingEasyMore difficult (smaller bend radius)
Hot ForgingEasySuitable
MachiningEasyModerate (higher hardness)
Drilling / PunchingEasyRequires more force
Galvanizing SuitabilityExcellentGood (pay attention to Si content)

S235 is easier to process in forming operations due to its low carbon content. Especially in cold bending applications, S235 allows for wider bending radii and has a lower risk of cracking. When cold bending with S355, attention should be paid to minimum bending radius values.

8. Corrosion Resistance and Protection

Both steel grades are unalloyed carbon steel, so there is no significant difference between them in terms of corrosion resistance. Both are susceptible to rusting if left unprotected and require protection:

Paint and coating systems: Long-lasting protection is achieved with primer + intermediate coat + top coat application.

Hot-dip galvanizing: Protection of 25–75 years is possible with zinc coating. S235 is more compatible with galvanizing; in S355, if the silicon content is high, the coating thickness may be uneven due to the Sandelin effect.

Mechanical protection: The risk of corrosion is reduced with proper drainage, ventilation, and moisture control.

9. Heat Treatment Behavior

S235 and S355 are structural steels and are generally not subjected to heat treatment for hardening purposes like heat-treatable steels. However, heat treatment may be applied in some cases:

Normalization: Applicable to both steels. Improves grain structure and provides homogeneous mechanical properties. A normalization temperature of 890–920°C is recommended for S235, and 880–910°C for S355.

Stress Relief: Annealing applied between 550–650°C to reduce internal stresses after welding. Especially recommended for S355 after thick welded joints.

Important: If you need special mechanical properties such as high hardness or wear resistance, you should consider heat-treatable or carburizing steels such as C45, 42CrMo4, or 16MnCr5 instead of S235 and S355. You can review our blog post “C45 vs 42CrMo4 vs 16MnCr5 Comparison” for more information.

10. Six Critical Questions for Choosing the Right Steel

You can determine the correct steel grade for your project by answering the following questions:

What loads will your structure be subjected to? High static and dynamic loads → S355. Low/medium loads → S235.
Is there intensive welding involved? Yes, and thick sections → S235 is more practical. Yes, but preheating is possible → S355 is feasible.
Is weight optimization necessary? Yes → S355 (thinner sections = lighter structure).
Is budget a priority? In the short term, S235 is more economical. In the long term, with section optimization, S355 may be more advantageous.
Will it operate in a cold environment? Yes → J2 or K2 suffix grades should be selected (valid for both grades).
What does your design code say? Eurocode, TS 500, or the project specification can determine the steel grade.

11. Summary Comparison Table

CriteriaS235 (St37)S355 (St52)
Yield Strength235 MPa355 MPa
Tensile Strength360–510 MPa470–630 MPa
Weldability★★★★★★★★★
Formability★★★★★★★★
Price (per kg)More economical5–15% higher
Section EfficiencyStandardSame strength with thinner sections
Corrosion ResistanceSame (protection required)Same (protection required)
Typical ApplicationsLight structures, general fabricationHeavy structures, bridges

12. Frequently Asked Questions (FAQ)

Are St37 and S235 the same steel?

Yes, they practically refer to the same steel. St37 is the older DIN standard designation; S235 is its equivalent in the current EN 10025 standard. There may be minor differences in chemical composition and mechanical properties, but they are considered equivalent in terms of application.

Can I use the S355 in place of the S235?

Yes, S355 is mechanically superior to S235 and has a higher load-carrying capacity. However, this may not always be necessary or economical. Using S355 in low-load structures leads to unnecessary cost increases.

Which type of steel should be used in earthquake zones?

Earthquake regulations generally prioritize the ductility properties of steel. Both types of steel can be used in earthquake zones, but connection details and structural design are the main factors determining earthquake performance. Design must comply with the requirements of TBDY 2018 (Turkish Building Earthquake Regulations).

Can I use the S235 and S355 together?

Yes, mixed use is possible and common in practice. For example, you can optimize both performance and cost by using S355 in the main load-bearing columns and S235 in secondary elements and purlins. However, the values ​​for lower-strength steel should be used in welded joints.

How can I verify the quality of the steel?

Request a Mill Test Certificate (MTC/3.1 Certificate) from your supplier. This document includes the chemical composition of the steel and the results of mechanical tests. At Uyar Çelik, we provide quality certificates conforming to EN standards for all our products.

13. Conclusion

Choosing between S235 (St37) and S355 (St52) is not a question with a single right answer. The correct choice is made by considering the loads the structure will be subjected to, welding requirements, budget, forming needs, and design codes together.

As a general rule: S235 should be preferred for lightweight structures, ease of processing, and budget priority; S355 should be preferred for high strength, heavy loads, and cross-section optimization.

At Uyar Çelik, with our half-century of experience, we manufacture and supply structural steel in accordance with the EN 10025 standard. For detailed information about our hot-rolled and cold-drawn steel bars produced in our facilities in Istanbul, Kocaeli, and Karabük, and for technical consultancy and price quotes, please contact us.

Let’s choose the right steel for your project together!
Uyar Steel’s expert engineering team helps you determine the most suitable steel grade for your project requirements. Contact us for free technical consultation and a price quote.
Phone:+90 (212) 485 9898 |Web:uyarcelik.com

Choosing the right steel between S235 (St37) and S355 (St52) is critical to the strength, cost, and long-term performance of your project. Uyar Steel expertise is here to help you secure your production process and determine the most suitable steel grade.

Contact us for customized steel and tolerance solutions for your project; the right material means the right result.

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10 Criteria to Consider When Choosing a Steel Supplier

Lama Demir ve Silme Demir Arasındaki Farklar Nelerdir?

10 Criteria to Consider When Choosing a Steel Supplier

Things to Consider When Choosing a Steel Supplier are not limited to price alone. Choosing a steel supplier is a strategic decision that directly impacts your production continuity, part quality, and total cost. Studies show that in the manufacturing sector, 50–60% of total production costs are determined by raw material supply.

The wrong choice can lead to production stoppages, quality issues, customer loss due to delivery delays, and high total costs in the long run. The right supplier, on the other hand, increases your production efficiency through supply security, consistent quality, competitive pricing, and technical support. For this reason, understanding the key things to consider when choosing a steel supplier is essential for building a sustainable and efficient production process.

1. Product Range Breadth

An ideal steel supplier should be able to offer hot-rolled (round, square, flat bar, hexagonal), cold-drawn (bright) bars, specialty steels (heat-treated, carburized, free-machining steels), and imported special alloy steels under one roof.

For example, a machine manufacturer might need hot-rolled S355JR square bar for chassis, cold-drawn C45 round bar for shafts, and cold-drawn 16MnCr5 round bar for gears. Being able to source these three different grades and forms from a single supplier simplifies logistics coordination, streamlines invoice management, and provides the advantage of bulk purchasing.

2. Material Certification and Traceability

EN 10204 Type 3.1 material certification is essential for steel supply. This certificate is an official document that independently verifies the heat number, chemical analysis results, mechanical test values, and dimensional measurements. Type 3.1 certification is particularly mandatory in the automotive, defense, hydraulic, and energy sectors. Ensure your supplier can provide complete certification for each batch and ensure traceability down to the heat number. This traceability is vital in recall situations.

Practical advice: Request a sample certificate and review its contents. A complete Type 3.1 certificate should include the heat number, tensile strength, yield strength, elongation percentage, hardness value, chemical analysis results for key elements such as carbon, manganese, and chromium, and dimensional measurement data. Certificates containing incomplete information may indicate weaknesses in the quality management system.

3. Stock Capacity and Variety

The cost of production line shutdowns is very high. Having a supplier with readily available stock in a wide range of sizes and grades is critical to meeting your urgent needs. Stock depth (diameter range, grade variety) and stock turnover rate should be evaluated. A supplier that can ensure supply security even during seasonal demand fluctuations will secure your production planning.

Ask these questions when evaluating stock: Is there a constant stock of your most frequently used diameters and grades? How long does it take to supply non-standard sizes? What is the minimum order quantity? Are you open to small batch orders? The answers to these questions reveal your operational flexibility.

4. Delivery Speed ​​and Logistics Structure

Delivery time is a crucial criterion, especially for companies using JIT (Just-in-Time) production. Suppliers capable of shipping from multiple locations offer shorter delivery times and lower transportation costs thanks to geographical proximity. Factors to consider include: warehouse and distribution center locations, standard delivery time, capacity to fulfill urgent orders, and transportation options. For example, a supplier in Turkey that can ship from different regions such as Istanbul, Kocaeli, and Karabük provides quick access to customers in the Marmara, Central Anatolia, and Black Sea regions.

5. Dimensional Accuracy and Tolerance Guarantee

Dimensional tolerances of bars directly impact your CNC machining costs. Verify that your supplier can offer products with tolerances conforming to EN standards (EN 10060, EN 10059, EN 10058, EN 10061, EN 10278) and guarantees these tolerances. For cold-drawn bars, a guaranteed tolerance class of h9 or h11 means less material removal, shorter machining times, and lower scrap. Length cutting, straightness, and ovality checks should also be included in the evaluation.

Verify tolerance compliance by taking measurements at the head, middle, and end of the bar using a caliper or micrometer. For round bars, check for ovality by measuring in two perpendicular directions across the same cross-section. Straightness is particularly important for long parts; deviations exceeding 0.5 mm/m can lead to holding problems and dimensional errors in CNC machining.

6. Technical Consulting and Engineering Support

They don’t just sell materials; they also offer technical consulting on the right quality selection. Especially in new projects or when considering material changes, the advice of an experienced technical team makes a significant difference. Whether you’re undecided between C45 and 42CrMo4, whether to choose carburizing or heat treatment, or need to perform a cost analysis between hot-rolled and cold-drawn steel, their ability to provide engineering support is a major advantage.

A technical team that can guide you on questions such as whether to choose heat-treated or carburizing steel, which heat treatment method is appropriate, or what the overall cost advantage of cold-drawn bar is compared to hot-rolled bar, significantly increases your supplier’s added value.

The supplier’s technical consulting capacity is directly related to their industry experience. A supplier with experience in different sectors such as automotive, hydraulics, machinery manufacturing, energy, and defense can offer you the most suitable solution by knowing the specific steel requirements and standards of each sector.

7. Price Transparency and Total Cost Approach

The lowest price per kilogram isn’t always the best offer. A total cost perspective should be adopted in price evaluation: unit price, shipping costs, minimum order quantity, payment terms, cutting service fee, and potential waste rate should all be considered together. Low-priced material with wide tolerances may incur extra machining costs in CNC machining.

For example, although the unit price of cold-drawn bar is 20-30% higher than hot-rolled bar, its tight tolerances and smooth surface in CNC machining can reduce the total part cost by 15-25%. The ability to offer such alternative solutions demonstrates that the company is a true solution partner.

8. Quality Management System and Certifications

Your supplier’s ISO 9001 quality management system certification demonstrates that their processes are standardized and that a culture of continuous improvement exists. For the automotive sector, IATF 16949 compliance, and for the defense industry, NATO AQAP standards should also be evaluated. In addition to certifications, internal quality control processes are also important: incoming material inspection, dimensional verification, surface inspection, and traceability systems should be examined.

The effectiveness of a quality management system is not measured solely by certification. Past performance, customer references, and reputation within the industry should also be considered. If possible, organize a visit to the supplier’s facility to observe warehouse conditions, measuring equipment, and quality control processes on-site. This visit allows you to assess operational capabilities that are not apparent on paper.

9. Flexibility and Capacity to Fulfill Special Orders

Your production needs don’t always fit standard molds. Suppliers who can offer flexible services such as custom size cutting, special tolerances, small batch orders, or urgent deliveries can save you from unexpected production requirements. Ask these questions in your evaluation: what is the minimum order quantity, can custom-sized bars be supplied, can you import non-standard grades, and what is the lead time for urgent orders?

Flexibility is also measured by communication speed and response time. Suppliers who can respond to your quotation requests the same day, share stock information instantly, and provide quick answers to your technical questions will increase your operational efficiency. Suppliers offering digital infrastructure and e-commerce integration stand out in this regard.

10. International Reach and Export Experience

A supplier integrated into a global supply chain is not limited to domestic sources; they can source special alloy steels from international markets and offer alternatives from different origins. The ability to import from Europe, CIS countries, or the Far East increases supply security. At the same time, a supplier with overseas locations (such as a Düsseldorf or European warehouse) provides a logistical advantage to exporting customers and guarantees compliance with international standards.

The ability to fulfill urgent orders is particularly critical. If a supplier can deliver within 24-48 hours in case of an unexpected material need on your production line, it can save you from production stoppages. Therefore, your supplier’s stock depth and shipping flexibility are decisive factors in a long-term business relationship.

With the European Union’s CBAM regulations, carbon footprint information has also become an important criterion in supply chains. Companies exporting to Europe will begin to demand product-based carbon emission data. Suppliers who are prepared for this change in advance will gain a strategic advantage in the future. From a sustainability perspective, your supplier’s environmental policies, energy efficiency efforts, and waste management practices should also be included in the evaluation.

Assessment Checklist

#CriteriaEvaluation Question
1Product rangeAre hot-rolled, cold-rolled, and engineering steels offered under one roof?
2Material certificationCan Type 3.1 certificates be provided for every batch?
3Stock capacityIs there a wide range of sizes and grades available in stock?
4Delivery speedIs fast shipment possible from multiple locations?
5Dimensional accuracyAre EN tolerances guaranteed with straightness control?
6Technical supportIs engineering support provided for material selection?
7Pricing transparencyAre quotes clear and based on total cost perspective?
8Quality systemIs it ISO 9001 certified? Does it meet industry standards?
9FlexibilityCan special sizes, tolerances, or urgent orders be handled?
10International reachDoes it have import/export capability and overseas storage?

Frequently Asked Questions (FAQ)

What is the most important criterion when choosing a steel supplier?

No single criterion is decisive; however, research in the manufacturing sector shows that quality, delivery reliability, and cost are the top three. In terms of quality, Type 3.1 certification is the most decisive sub-criterion; in terms of delivery, stock capacity and multiple locations are key; and in terms of cost, the total cost perspective is the most crucial.

Should I choose a single source or multiple suppliers?

Receiving supplies from a single source may offer a price advantage, but it creates supply risk. The ideal approach is to establish a strong primary partnership, but always keep an alternative supplier readily available.

What criteria are a priority for small-scale producers?

For small-scale manufacturers, low minimum order quantities, custom cutting services, and fast delivery are top priorities. Additionally, technical consulting support is invaluable for companies that do not have their own engineers.

How can I measure supplier performance?

Create a supplier scorecard and conduct periodic evaluations. Key performance indicators include: on-time delivery rate, quality non-conformity rate, completeness of certifications, price stability, and speed of communication. Tracking these metrics quarterly or semi-annually allows for continuous improvement.

Conclusion: 10 Criteria to Consider When Choosing a Steel Supplier

Finally, it’s important to view the evaluation process not as a one-off event, but as a continuous improvement cycle. Create scorecards every three or six months, tracking metrics such as on-time delivery rate, number of quality nonconformities, complete certifications, and price stability. This data-driven approach continuously strengthens your supplier relationship and reinforces long-term business partnerships.

This is not just a price comparison; it’s a strategic assessment encompassing quality, supply security, technical competence, and long-term business partnership potential. The 10 criteria in this guide will help you structure your evaluation process and select the most suitable supplier.

Remember: the best choice isn’t the cheapest, but the one that minimizes total cost, guarantees quality, and ensures production continuity.

By systematically applying these 10 criteria, you can strengthen your supply chain, ensure production continuity, and gain a competitive advantage. Supplier selection is not a one-off event, but a continuous evaluation and development process. A strong, well-established business partnership means not only raw material supply but also the sharing of technical knowledge, market information, and innovation.

As Uyar Çelik, we offer a wide range of hot-rolled, cold-drawn, and high-quality steel bars, Type 3.1 certification, fast delivery from Istanbul, Karabük, Kocaeli, and Düsseldorf locations, and technical consultancy services.

For detailed information and a quote:

 www.uyarcelik.com/iletisim

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What Is Heat Treatment in Steel? Annealing, Quenching, Tempering, and Carburizing Guide

What Is Heat Treatment in Steel? Annealing, Quenching, Tempering, and Carburizing Guide

What Is Heat Treatment in Steel? Annealing, Quenching, Tempering, and Carburizing Guide

Heat treatment in steel is a general term for controlled heating and cooling processes applied to steel materials to alter their mechanical properties—such as hardness, strength, toughness, wear resistance, and machinability. As explained in this Annealing, Quenching, Tempering, and Carburizing Guide, the correct heat treatment process can significantly increase the service life of a steel part, while an incorrect application can render it unusable.

At Uyar Çelik, with our half-century of experience in steel production, we offer our customers not only high-quality raw materials but also technical support in selecting and processing the right materials. In this guide, titled What Is Heat Treatment in Steel? Annealing, Quenching, Tempering, and Carburizing Guide, we detail the most commonly used heat treatment methods in the industry, their application parameters, and which treatment is suitable for which steel grade.

1. What is Heat Treatment and Why is it Necessary?

Heat treatment refers to thermal processes applied to steel to alter its internal structure (microstructure). Steel transforms into different crystal structures at different temperatures; these transformations are controlled to obtain the desired mechanical properties.

Basic Purposes of Heat Treatment

To increase hardness: For parts requiring wear resistance (gears, shafts, molds)
To increase strength: To provide higher load-carrying capacity
To improve toughness: To increase impact resistance by reducing brittleness
To facilitate machinability: To prepare for machining or cold forming
To relieve internal stresses: To reduce stresses that occur after welding, rolling, or forging
To homogenize the microstructure: To obtain consistent properties by smoothing the grain structure

Phase Transformations: Basic Concepts

PhaseFormation ConditionProperties
FerriteSlow coolingSoft, ductile, low hardness. The room-temperature structure of pure iron.
PearliteSlow coolingA lamellar structure of ferrite and cementite. Offers medium hardness and strength.
AusteniteHigh temperature (>723°C)Face-centered cubic structure. A paramagnetic phase capable of dissolving carbon.
MartensiteRapid cooling (quenching)Very hard and brittle. Forms by the sudden cooling of austenite.
BainiteModerate cooling rateProperties between martensite and pearlite. Provides a good balance of hardness and toughness.
Cementite (Fe₃C)Compound with carbonIron carbide. Very hard but brittle.

2. Annealing

Annealing is the process of heating steel to a specific temperature, holding it at that temperature for a sufficient period, and then slowly cooling it (usually inside a furnace). The aim is to soften the steel, improve its machinability, and relieve internal stresses.

Types of Annealing

Full Annealing

Heated to 30–50°C above the upper critical temperature (Ac3) and slowly cooled in the furnace. The result is a fine-grained, homogeneous ferrite-pearlite structure. This process is particularly applied to correct the microstructure in castings and forgings.

Spheroidizing

In high-carbon steels (C > 0.6%), the hard and brittle cementite lamellae are spheroidized to improve machinability. The steel is held for an extended period just below or above the Ac1 temperature. Frequently applied to mold steels and spring steels.

Stress Relief Annealing

Performed to reduce internal stresses that occur after welding, machining, or cold forming. The steel is heated to 550–650°C, held at this temperature for 1–2 hours, and slowly cooled. There is no phase transformation; only stresses are relieved.

Homogenization Annealing (Diffusion Annealing)

This process is applied to eliminate chemical composition differences (segregation) that occur during casting. The steel is heated to high temperatures such as 1050–1200°C and held at this temperature for a long time. Then, normalization annealing is performed to refine the coarse grains.

Annealing Application Table

Steel GradeTemperature (°C)DurationPurpose
C45 (1.0503)800–8501–2 hoursMachinability, stress relieving
42CrMo4 (1.7225)820–8601–2 hoursSoftening, preparation for machining
16MnCr5 (1.7131)830–8601–2 hoursPreparation before carburizing
100Cr6 (1.3505)780–8102–4 hoursSpheroidizing annealing, machinability
S235/S355550–6501–2 hoursPost-weld stress relieving

3. Normalization

Normalization is the process of heating steel to 30–50°C above its Ac3 temperature, holding it for a sufficient time, and then cooling it in still air. Unlike full annealing, cooling occurs in air, not in a furnace. The result is a finer-grained and slightly harder structure compared to annealing.

Purposes of Normalization:

To homogenize the irregular grain structure formed after rolling, forging, or casting.

To balance mechanical properties (strength + toughness).

To prepare for subsequent heat treatments (hardening, carburizing).

To be used as a final heat treatment in low and medium carbon steels.

Application: The normalization temperature for C45 steel is 840–870°C, and for 42CrMo4 it is 850–880°C. A holding time of approximately 1 hour is recommended for every 25 mm of part thickness.

4. Quenching / Hardening

Quenching is a fundamental method for achieving hardness in steel. The steel is heated to the austenitizing temperature (Ac3 + 30–50°C), held at this temperature, and then rapidly cooled (with water, oil, polymer, or air). Rapid cooling prevents the transformation of austenite into pearlite and allows the formation of a very hard martensite structure.

Cooling Media and Their Effects

MediumCooling RateHardness EffectApplication Area
WaterVery highMaximum hardnessCarbon steels, low alloy steels
OilHighHigh hardnessQuenched and tempered steels (42CrMo4, C45)
PolymerAdjustableControlled hardnessPrecision parts, complex geometries
Air / GasLowMedium hardnessHigh alloy steels, tool steels
Salt BathMediumUniform hardnessSmall-section, alloyed parts

Hardening Application Table

Steel GradeAustenitizing Temperature (°C)Quenching MediumResulting Hardness
C45820–860Water or oil55–58 HRC
42CrMo4830–860Oil54–58 HRC
16MnCr5830–860Oil60–62 HRC (surface)
100Cr6830–850Oil62–65 HRC
1.2379 (D2)1000–1030Air or oil58–62 HRC
1.2344 (H13)1000–1040Air or oil48–54 HRC
Important: After quenching, steel becomes extremely hard and brittle. In this condition, it is not suitable for direct use. A tempering process must always be applied afterward. A quenched but untempered steel component can easily fracture under even minor impact.

5. Tempering

Tempering is a mandatory heat treatment applied immediately after quenching (hardening). The aim is to reduce the excessive brittleness of hardened steel and to establish an optimum balance between hardness and toughness.

Process: After quenching, the steel is reheated below the Ac1 temperature (between 150–650°C), held at this temperature for 1–2 hours, and cooled in air, oil, or water. As the tempering temperature increases, hardness decreases and toughness increases.

Tempering Temperature Ranges and Effects

Temperature RangeResultTypical Applications
150–250°CHigh hardness is retained, with a slight increase in toughnessCutting tools, dies, bearings, measuring instruments
250–400°CMedium hardness, increased elasticitySprings, pins, tools such as axes and knives
400–650°CHardness decreases significantly, toughness reaches its maximumQuenched and tempered steels (C45, 42CrMo4): shafts, gears, axles
Important warning: In some steels, tempering within the 250–370°C range may cause a risk of temper embrittlement. This temperature range should be avoided as much as possible or passed through quickly.

6. Improvement Process (Quenching + Tempering = Q&T)

Heat treatment is the combined application of quenching and tempering. The combination of hardening and high-temperature tempering (mostly 450–650°C) provides high strength, good toughness, and superior fatigue resistance.

Heat treatment takes its name from the “heat-treatable steels” specifically developed for this process. Medium-carbon, alloy steels such as C45, 42CrMo4, and 34CrNiMo6 belong to this group. Heat treatment is standard practice in shafts, axles, crankshafts, gearboxes, and machine parts requiring high strength.

Uyar Çelik’s range of high-quality steels such as C45, 42CrMo4, and 16MnCr5 have chemical compositions suitable for heat treatment. For a detailed comparison, please see our blog post “C45 vs 42CrMo4 vs 16MnCr5 Comparison”.

7. Cementation (Carburizing) — Surface Hardening

PhaseFormation ConditionProperties
FerriteSlow coolingSoft, ductile, low hardness. The room-temperature structure of pure iron.
PearliteSlow coolingLamellar structure of ferrite and cementite. Medium hardness and strength.
AusteniteHigh temperature (>723°C)Face-centered cubic structure. A paramagnetic phase capable of dissolving carbon.
MartensiteRapid cooling (quenching)Very hard and brittle. Formed by the sudden cooling of austenite.
BainiteModerate cooling rateProperties between martensite and pearlite. Good balance of hardness and toughness.
Cementite (Fe₃C)Compound with carbonIron carbide. Very hard but brittle.

Case-hardening steels

Case hardening is applied to low-carbon steels with a carbon content between 0.10% and 0.25%. Examples:

16MnCr5 (1.7131): The most common case hardening steel. Used in the production of gears, pins, and camshafts.
20MnCr5 (1.7147): Higher hardenability. Preferred in large-section gears.
18CrNiMo7-6 (1.6587): High performance. Used in aerospace and automotive transmission gears.

The surface hardness after case hardening is typically in the range of 58–63 HRC, while the core hardness remains around 30–40 HRC. The case hardening depth (CHD) is usually between 0.5–2.0 mm.

8. Other Surface Hardening Methods

8.1. Nitriding

Nitriding is a hardening process applied to the surface of steel by diffusion of nitrogen. Because it is applied at low temperatures such as 500–580°C, minimal deformation occurs in the part. Quenching is not required after nitriding; the surface hardens directly.

Surface hardness can reach 1000–1200 HV. Wear resistance, corrosion resistance, and fatigue strength are significantly increased. Steels containing aluminum, chromium, and molybdenum (such as 42CrMo4, 34CrAlNi7) are the most suitable grades for nitriding.

8.2. Induction Curing

Induction hardening is a process where the surface of a part is rapidly heated locally using an electromagnetic field, followed by quenching to harden it. Unlike carburization, it achieves hardness using only the existing carbon content without altering the chemical composition.

For induction hardening, the carbon content of the steel must be at least 0.35–0.50%. Medium carbon steels such as C45 and 42CrMo4 are ideal for this process. It is widely used in the automotive industry for hardening crankshafts, camshafts, gears, and shafts.

9. Which heat treatment is applied to which steel grade?

Steel GradeSteel GroupRecommended Heat Treatments
S235 / S355StructuralNormalizing, stress relieving annealing
C45Quenched & TemperedQuenching & tempering, normalizing, induction hardening
42CrMo4Quenched & TemperedQuenching & tempering, nitriding, induction hardening
16MnCr5Carburizing SteelCarburizing + quenching, normalizing
100Cr6Bearing SteelSpheroidizing annealing, hardening + low tempering
1.2379 (D2)Cold Work Tool SteelHardening (air/oil) + multiple tempering
1.2344 (H13)Hot Work Tool SteelHardening + tempering (2–3 times), nitriding
51CrV4Spring SteelQuenching & tempering, stress relieving

10. Common Mistakes and Precautions in Heat Treatment

  1. Failure to Temper After Quenching

    The most critical mistake. Quenched steel is extremely brittle and can crack suddenly during use. Tempering should be done as soon as possible after quenching (ideally within 1 hour).

    Incorrect Temperature Selection

    If the austenitizing temperature is too low, complete austenitization cannot be achieved, and hardness will be insufficient. If it is too high, grain coarsening occurs, and toughness decreases.

    Insufficient Holding Time

    It takes time to reach a homogeneous temperature to the center of the part. Insufficient holding time leaves untransformed areas in the center. As a general rule, a holding time of 1 hour should be applied for every 25 mm of wall thickness.

    Incorrect Cooling Medium Selection

    If carbon steel is quenched in oil, sufficient hardness may not be obtained. If alloy steel is quenched in water, excessive internal stress and cracking risk occur. Selecting a cooling medium appropriate to the steel grade is vital.

    Oxidation and Decarburization

    In heat treatment without a protective atmosphere, the steel surface oxidizes (scale forms) and loses carbon. This reduces surface hardness. Controlled atmosphere or vacuum ovens prevent this problem.

Frequently Asked Questions (FAQ)

Can heat treatment be applied to all types of steel?

No. For hardening, the steel must have a sufficient carbon content (usually min. 0.30–0.35%). Low-carbon structural steels (S235, S355) cannot be hardened; they can be subjected to normalization or stress-relieving annealing.

What is the difference between heat treatment and hardening?

Hardening (quenching) is a single-stage process aimed solely at achieving hardness. Heat treatment, on the other hand, is a combination of hardening and high-temperature tempering. Heat treatment provides both high strength and good toughness simultaneously.

What is the difference between cementation and nitriding?

In cementation, carbon is impregnated into the surface and then quenched with water (900–950°C). In nitriding, nitrogen is impregnated into the surface and quenching is not necessary (500–580°C). Since nitriding is done at a lower temperature, the risk of deformation is very low, but the hardening depth is shallower.

Which heat treatment should be applied to 42CrMo4 steel?

42CrMo4 is a heat-treatable steel. Standard application: austenitizing at 830–860°C → quenching in oil → tempering at 540–660°C. The result is a hardness of approximately 280–320 HB and high tensile strength (900–1100 MPa). Nitriding and induction hardening can also be applied.

Will the part change dimensions after heat treatment?

Yes. Dimensional changes are inevitable due to phase transformations and thermal expansion/contraction. Martensite formation causes approximately a 1% volume increase. Therefore, post-heat treatment planning, such as grinding or honing, should be done for precision parts.

Conclusion: What is Heat Treatment in Steel?

Heat treatment is a critical engineering process with the power to determine the performance of parts. Annealing for softening, normalization for homogenization, quenching for hardening, tempering for toughening, and carburizing for surface hardening—each addresses a different need.

The correct heat treatment application begins with the correct steel selection. At Uyar Çelik, with our half-century of experience, we produce heat-treatable steels, carburizing steels, and high-quality industrial steels in accordance with EN and ASTM standards. Our steel bars, produced in our modern facilities in Istanbul, Kocaeli, and Karabük, ensure consistent and reliable results for our customers in their heat treatment processes.

Let’s determine the right steel grade for your project together!

Uyar Çelik’s technical team will help you choose the most suitable steel grade for your heat treatment requirements. Contact us for technical consultation and a price quote on our range of heat-treatable steel bars.

Phone:

 +90 (212) 485 9898  |  Web: uyarcelik.com

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The Most Suitable Steel Grades for CNC Machining: A Guide to Machining

The Most Suitable Steel Grades for CNC Machining: A Guide to Machining

 

CNC machining is the backbone of the modern manufacturing industry. From the automotive sector to the defense industry, and from machinery manufacturing to hydraulic systems, the production of precision parts is carried out on CNC machines across countless sectors. In this context, The Most Suitable Steel Grades CNC Machining play a decisive role in overall production efficiency, quality, and cost control. However, the success of CNC machining depends on the selection of the right steel—even more so than on the machine’s capabilities.

If the wrong steel grade is selected, tool life is reduced, surface quality deteriorates, scrap rates increase, and total production costs rise. Conversely, the right steel selection shortens machining time, extends tool life, improves surface quality, and reduces the cost per part.

1. Why is Steel Selection Critical in CNC Machining?

CNC machines operate with micron-level precision, but this precision only becomes meaningful when the properties of the material being machined are suitable. Steel selection affects CNC machining performance through the following fundamental parameters:

Machinability: This refers to how easily and efficiently the steel can be machined with a cutting tool. High machinability allows for higher cutting speeds and longer tool life.


Hardness: As hardness increases, machinability decreases. However, a certain level of hardness is necessary for the strength of the final part. Ideal steel selection balances these two parameters.


Chip Form: Steels that produce short and brittle chips create fewer problems in CNC automation systems. Long and coiled chips can cause machine downtime and surface defects.


Dimensional Stability: Cold-drawn steels offer a narrower tolerance range compared to hot-rolled alternatives, providing predictable results in CNC machining.


Surface Quality: The internal structure and inclusion distribution of the steel directly affect the resulting surface roughness.

2. Most Commonly Used Steel Categories in CNC Machining

Steels used for machining can be examined in four main categories:

2.1. Free-Cutting Steels

Free machining steels are a group of steels specifically developed for CNC machining. Their high sulfur content (mostly in the range of 0.15–0.35%) and, in some grades, the addition of lead or bismuth, ensures that the chips are brittle and short. This allows for smooth machining at high cutting speeds.

The most common free machining steel grades are: 11SMn30 (1.0715) for general-purpose free machining, 11SMnPb30 (1.0718) with lead addition, offering the highest machinability (although its use is decreasing due to RoHS restrictions), 44SMn28 (1.0762) for free machining applications requiring higher strength, and 46S20 (1.0727) as a medium-carbon free machining steel.

Free machining steels are widely used, particularly in automotive spare parts, fasteners, valve bodies, hydraulic fittings, and mass production of CNC lathes.

2.2. Quenched and Tempered Steels

Heat-treatable steels are a group of steels that achieve a combination of high strength and toughness through quenching and tempering heat treatment. CNC machining is usually performed after heat treatment, and these steels operate within a tensile strength range of 800–1200 MPa.

The main heat-treatable steel grades are: C45 (1.0503), the most common general-purpose heat-treatable steel, used in shafts, axles, and medium-strength machine parts. 42CrMo4 (1.7225), a chromium-molybdenum alloy, offers high strength and toughness; it is preferred in crankshafts, gear shafts, and heavy-duty parts. 34CrNiMo6 (1.6582) is the highest strength heat-treatable steel grade and is used in aerospace, defense, and energy sector applications.

Important note: Heat-treatable steels have lower machinability compared to free-machining steels. CNC machining parameters (speed, feed rate, depth of cut) must be carefully optimized. Carbide tools and the use of appropriate coolant are essential.

2.3. Case-Hardening Steels

Case-hardening steels are a group of steels designed to produce parts with a hard outer surface and a tough inner core. Their low carbon content (mostly 0.10–0.20% C) allows them to perform well in CNC machining. Carburization is usually applied after CNC machining.

16MnCr5 (1.7131) and 20MnCr5 (1.7147) are the most common case-hardening steels. They are used in parts requiring wear resistance, such as gears, camshafts, pins, and synchronizer rings. After CNC machining to achieve dimensional accuracy, the surface hardness is increased to 58–62 HRC through a case-hardening process.

2.4. Structural Steels

Structural steels such as S235JR and S355JR are used in simpler applications in CNC machining. They are preferred for machined surfaces of machine frames, support elements, and welded structures where strength requirements are low to medium. Their low cost and ease of machining are their greatest advantages.

3. Comparison of CNC Machinability of Steel Grades

The table below compares the most commonly used steel grades in CNC machining based on their machinability, hardness, and typical applications:

Steel GradeGroupMachinabilityHardness (HB)Typical CNC Applications
11SMn30Free-cuttingVery High140–180Mass production turned parts, fasteners, valve components
11SMnPb30Free-cuttingHighest140–180High-speed automatic turning, precision connectors
C45Quenched & temperedMedium200–260Shafts, axles, machine parts, pins
42CrMo4Quenched & temperedMedium-Low250–320Crankshafts, gear shafts, high-strength bolts
16MnCr5Case hardeningHigh150–200Gears, pins, camshafts, synchronizer rings
20MnCr5Case hardeningHigh160–210Large gears, heavy load-bearing shafts
S355JRStructuralHigh130–170Machine bodies, support parts, frames

4. Soğuk Çekilmiş Çeliğin CNC İşlemede Sağladığı Avantajlar

In CNC machining, raw material form is as important a selection criterion as quality. Cold-drawn steel bars offer significant advantages in CNC machining compared to hot-rolled alternatives:
ParameterHot RolledCold Drawn
Tolerance rangeIT 13–14 (wide)h9–h11 (tight)
Surface roughness (Ra)6.3–12.5 µm0.8–3.2 µm
Pre-CNC preparationScale removal + rough turning requiredReady for direct machining
Material removal amountHigh (wide tolerance compensation)Low (near-net starting size)
Tool wearHigh (scale and surface irregularities)Low (homogeneous surface)
Total part costLow material cost, high machining costHigher material cost, lower machining cost → generally advantageous

Practical tip: In medium to high-volume CNC production, using cold-drawn bar can reduce the total cost per part by 15–25%. Cold-drawn round, square, and hexagonal steel bars are particularly ideal raw materials for CNC turning and milling applications.

5. Factors Affecting Steel Selection in CNC Machining

When determining the correct steel grade, the following factors should be systematically evaluated:

5.1. Functional Requirements of the Final Part

The operating conditions of the part are the primary factor determining steel selection. While S355JR or C45 are sufficient for parts subjected to static loads, high-strength heat-treatable steels such as 42CrMo4 or 34CrNiMo6 are required for parts exposed to dynamic and impact loads. If wear resistance is critical, carburizing steels (16MnCr5) are preferred.

5.2. Production Volume and Automation Level

In mass production CNC sliding automatic lathes and multi-spindle lathes, chip reduction is of critical importance. For these machines, automatic lathe steels (11SMn30, 44SMn28) are by far the most efficient option. However, for single-piece or small-batch CNC machining, steel selection may be more flexible.

5.3. Heat Treatment Requirement

If steel is to be heat-treated, the machining sequence is critically important. For carburizing steels, CNC machining is usually performed first, followed by carburization. For heat-treatable steels, heat treatment is usually performed first, followed by finishing CNC machining. This sequence ensures dimensional stability.

5.4. Cost-Performance Balance

Choosing the highest quality steel isn’t always the most economical solution. For example, using 42CrMo4 for a simple flat pin might create unnecessary costs, while C45 can perform the same function at a much lower cost. The key approach: “The simplest steel that suffices is the best steel.”

Hardening Application 6. Relationship Between Cutting Parameters and Steel Quality in CNC Machining Connection Table

Steel quality directly determines the cutting parameters to be applied on a CNC machine. Incorrect parameter selection can lead to tool breakage, poor surface finish, or excessively high chip temperatures.

General rules: High cutting speeds (Vc 120–200 m/min) and high feed rates are applicable to free-machining steels. Medium cutting speeds (Vc 100–160 m/min) are recommended for medium-carbon steels such as C45. Lower cutting speeds (Vc 80–140 m/min) and special carbide tools are required for alloyed heat-treatable steels such as 42CrMo4. Case-hardening steels (pre-heat-treated) can be machined at relatively high speeds due to their low carbon content.

Tool selection: Coated carbide tools (TiN, TiAlN, AlCrN) should be preferred for high-hardness steels (above 250 HB). For free-machining steels, even HSS (High-Speed ​​Steel) tools can provide sufficient performance.

7. Sectoral Application Examples

  • Automotive Suppliers: Gear shafts (42CrMo4), synchronizer rings (16MnCr5), hydraulic fittings (11SMn30)

  • Hydraulics and Pneumatics: Piston shafts (42CrMo4 or C45, chrome plated), valve bodies (11SMn30), cylinder heads (S355JR)

  • General Machinery Manufacturing: Bearing housings (C45), coupling parts (42CrMo4), belt pulley (S355JR)

  • Defense Industry: High-strength shaft and axle parts (34CrNiMo6), gearbox components (20MnCr5)

  • Energy Sector: Turbine shafts (42CrMo4), flange parts (S355JR), wind turbine components (34CrNiMo6)

8. Points to Consider When Sourcing Steel for CNC Machining

  • Material certification (EN 10204 Type 3.1): CNC machining companies, especially in automotive and aerospace projects, require 3.1 certification for material traceability. Ensure your supplier can provide this document.

  • Dimensional accuracy: Check the tolerance class of cold-drawn bars. h9, h10, or h11 tolerance determines the pre-CNC preparation requirement.

  • Flatness and ovality: Curvature and ovality in bar materials can cause problems during chuck clamping on a CNC machine. Ask your supplier for a flatness guarantee.

  • Stock variety: A supplier offering a wide range of sizes in round, square, flat bar, and hexagonal profiles can be a single source for your various CNC projects.

  • Cutting service: Suppliers offering cut-to-length services shorten your CNC preparation process and reduce raw material waste.

Frequently Asked Questions (FAQ)

What is the best steel for CNC lathes?

For mass CNC lathe production, automatic machining steels (11SMn30, 11SMnPb30) offer the highest efficiency. When higher strength is required, C45 or 42CrMo4 can be preferred, but the cutting parameters must be adjusted accordingly.

Can 42CrMo4 be machined with a CNC machine?

Yes, 42CrMo4 can be successfully machined with CNC. However, due to its high alloy content, it requires lower cutting speeds and coated carbide tools compared to other free-machining steels. Careful parameter adjustment is essential, especially in post-heat treatment machining.

Why is cold-drawn steel preferred for CNC machining?

Cold-drawn steel provides a tight tolerance range (h9–h11), smooth surface finish, and dimensional consistency. These properties translate to less material removal, shorter setup times, and lower scrap rates in CNC machining. Ultimately, this reduces the total cost of the part.

Which heat treatment should be applied to 42CrMo4 steel?

42CrMo4 is a heat-treatable steel. Standard application: austenitizing at 830–860°C → quenching in oil → tempering at 540–660°C. The result is a hardness of approximately 280–320 HB and high tensile strength (900–1100 MPa). Nitriding and induction hardening can also be applied.

Why is cold-drawn steel preferred for CNC machining?

Cold-drawn steel provides a tight tolerance range (h9–h11), smooth surface finish, and dimensional consistency. These properties translate to less material removal, shorter setup times, and lower scrap rates in CNC machining. Ultimately, this reduces the total cost of the part.

Future Trends in CNC Machining

The CNC machining industry continues to evolve rapidly with technological advancements and industrial transformations. These changes directly impact steel selection and supply strategies.

AI-powered cutting optimization allows CNC machines to adjust cutting parameters in real-time according to material properties. This enables more predictable results across different steel grades. The widespread adoption of minimum quantity lubrication (MQL) technology increases expectations for steel surface quality, leading to a higher preference for cold-drawn bars.

Furthermore, the trend towards lead-free free-machining steels is accelerating. European Union RoHS and REACH regulations restrict the use of lead-containing grades such as 11SMnPb30. Bismuth-containing free-machining steels and improved grades based on 11SMn30 are emerging as alternatives. Considering these environmental compliance criteria in supplier selection is critical for long-term business partnerships.

Industry 4.0 and digital twin technologies allow for the simulation of the entire CNC machining process in a virtual environment. These simulations use the chemical composition, hardness, and machinability data of the steel as input. Therefore, the ability of suppliers to provide material data in digital format will be a significant factor in gaining a competitive advantage in the future.

Conclusion: Discover the most suitable steel grades for CNC machining, their machinability characteristics, and the correct material selection for chip removal in this guide.

Steel selection in CNC machining is a strategic decision that directly affects part quality, production speed, and cost. The four main steel categories we discuss in this guide—free-machining, heat-treatable, carburizing, and structural steels—respond to different application areas and production requirements.

To choose the right steel, evaluate your production volume and level of automation, clearly define the functional requirements of the final part, consider cold-drawn as an alternative to hot-rolled from a total cost perspective, and request dimensional assurance from your supplier along with EN 10204 Type 3.1 certification.

As Uyar Çelik, we offer a wide range of hot-rolled, cold-drawn, and high-quality steel bars (round, square, flat bar, hexagonal) to CNC machining companies.

Contact us for EN standard compliant, Type 3.1 certified material supply from our locations in Istanbul, Karabük, Kocaeli, and Düsseldorf.

For detailed information and a quote:

 www.uyarcelik.com/iletisim

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Steel Bars Used in Hydraulic Cylinder Manufacturing and Selection Criteria

Steel Bars Used in Hydraulic Cylinder Manufacturing and Selection Criteria

Hydraulic cylinders play a critical role across all sectors of industry, from construction machinery to agricultural equipment, and from press systems to marine applications. The performance, service life, and reliability of a hydraulic cylinder depend largely on the quality of the steel bars used. Steel Bars Used in Hydraulic Cylinder Manufacturing and Selection Criteria are therefore among the most important factors affecting long-term system performance.

Steel bars used in components such as the piston rod, cylinder barrel, and connecting elements are subjected to high pressure, repeated loads, corrosive environments, and tight tolerance requirements. Incorrect steel selection can lead to premature fatigue failure, seal damage, chrome plating delamination, and ultimately costly system failures.

In this guide, we examine in detail the steel bars used in hydraulic cylinder production, quality selection criteria, chrome plating compatibility, and key considerations during the procurement process.

1. Basic Components of a Hydraulic Cylinder and Steel Requirements

A hydraulic cylinder consists of several main components with different mechanical requirements. Each component requires different steel properties:

Piston Rod (Chrome Bar): This is the cylinder’s reciprocating element. Surface hardness, corrosion resistance, straightness, and tight tolerances are the most critical requirements. The applicability of hard chrome plating is the primary determinant of steel selection.
Cylinder Body Tube: This is the main structural element that carries hydraulic pressure. The internal surface quality achieved through honing directly affects seal performance. Seamless steel tubes (ST52, E355) are typically used.
Piston and Cover Components: In these parts, which are manufactured via CNC machining, machinability and dimensional accuracy are paramount. Grades such as C45 or S355JR are commonly used.
Connecting Elements (Joints, Ears): In these components, which are subjected to impact loads, toughness and fatigue resistance are of critical importance.

2. Steel Bar Grades Used for Piston Shafts

The piston rod is the most critical component of a hydraulic cylinder. Since it operates both inside and outside the cylinder, it must simultaneously withstand mechanical loads, meet sealing requirements, and endure environmental conditions. The table below compares the most commonly used steel grades in piston rod manufacturing:
Steel GradeEN EquivalentStrength (MPa)Chrome Plating CompatibilityTypical Application Area
C45 / CK451.0503580–700ExcellentStandard hydraulic cylinders, medium pressure applications
42CrMo41.7225900–1200ExcellentHigh-pressure cylinders, heavy machinery
20MnV61.5217550–700Very goodMicroalloyed, non-heat-treated usage
S355J21.0577470–630GoodLow–medium pressure, cost-effective solutions
AISI 3161.4401515–690Not requiredMarine, food, chemical industry

2.1. C45 / CK45: Industry Standard

C45 (DIN: CK45) is the most widely used steel grade worldwide for the production of hydraulic piston rods. Its medium-carbon composition (typically 0.42–0.50% C) provides an ideal substrate for hard chrome plating. When supplied in cold-drawn, ground, and polished form, the surface roughness prior to chrome plating reaches a range of Ra 0.2–0.4 µm. For standard industrial hydraulic cylinders requiring operating pressures up to 250 bar, C45 offers an optimal cost-performance balance.

2.2. 42CrMo4: High Performance

42CrMo4 is a high-strength quenched and tempered steel preferred for hydraulic cylinders operating under heavy-duty conditions. This chromium-molybdenum alloy provides a tensile strength of 900–1200 MPa after quenching and tempering. Mining equipment, heavy-duty presses, concrete pumps, and high-pressure (350–700 bar) industrial cylinders require this grade. When combined with induction hardening, 42CrMo4 can achieve a surface hardness of HRC 55–60 and provides superior wear protection under a chromium coating.

2.3. 20MnV6: A Microalloyed Alternative

20MnV6 is a modern steel grade that offers mechanical properties comparable to C45 without requiring heat treatment, thanks to its vanadium microalloy. The elimination of heat treatment costs reduces the total cost of the piston rod. Additionally, its good weldability provides an advantage in articulated piston rod designs. The use of 20MnV6 has increased significantly in recent years among European hydraulic cylinder manufacturers.

3. Cold-Drawn Bar: An Essential Component in Hydraulic Cylinder Manufacturing

In the production of hydraulic piston rods, cold-drawn steel bars offer significant advantages over their hot-rolled counterparts:

Precise tolerances (h8–h11): The tight tolerance range achieved after the cold-drawing process minimizes the need for machining in piston rod production. This reduces both labor costs and material waste.
Smooth surface (Ra 0.8–3.2 µm): The success of the chrome plating process is directly related to the quality of the substrate. The homogeneous surface of cold-drawn bars ensures the formation of a chrome layer with uniform thickness and high adhesion strength.
Straightness guarantee: Piston rod straightness is critical for seal life and sealing performance. Cold-drawn bars are typically supplied with straightness values of 0.5 mm/m or better.
Homogeneous microstructure: The refinement of the crystal structure during cold drawing ensures consistent mechanical properties throughout the bar. This is particularly important for long-stroke cylinders.

From a cost analysis perspective, although the unit price of cold-drawn bars is 20–30% higher than that of hot-rolled alternatives, it generally results in a 15–20% savings in total piston rod production costs. This savings stems from fewer grinding operations, shorter CNC machining times, a lower scrap rate, and the elimination of the need for additional surface preparation prior to chrome plating. This cost advantage becomes significantly more pronounced in high-volume production.

The profile shape is also important when selecting cold-drawn bars. In hydraulic piston rod production, nearly all applications use round steel bars. The diameter range typically varies between 20 mm and 200 mm; the most common diameters fall within the 30–100 mm range. Lengths are standardly supplied in 3-meter and 6-meter bars, but suppliers offering custom cutting services significantly enhance production efficiency.

4. The Relationship Between Chromium Plating and Steel Quality

Hard chrome plating is a critical process that enhances the surface hardness, wear resistance, and corrosion protection of hydraulic piston rods. The quality of the chrome layer and the success of the induction hardening process, if applied, depend on the properties of the underlying steel substrate.

Chrome plating thickness typically ranges from 20 to 50 micrometers. While 25 micrometers is common in standard industrial applications, thicknesses of 40 to 50 micrometers may be used in harsh marine and mining environments. Surface preparation prior to chrome plating consists of grinding (target Ra 0.2–0.4 µm), polishing, and cleaning.

Important technical note: Carbon and alloy steels such as C45 and 42CrMo4 exhibit excellent compatibility with hard chrome plating. Stainless steels, however, require a different chrome plating process, and their inherent corrosion resistance is typically utilized instead of chrome plating.

5. Selection of Steel for the Cylinder Body Tube

The cylinder body tube must safely withstand the operating pressure and provide an excellent internal surface finish to ensure smooth piston movement. ST52 (E355+N) is the most commonly used seamless steel tube grade in the production of hydraulic cylinder bodies. After honing, the internal surface roughness is brought to the range of Ra 0.2–0.4 µm.

The wall thickness calculation for selecting a cylinder tube is based on the operating pressure and safety factor. The Barlow formula (P = 2St/D) is the basic calculation method; here, P is the operating pressure, S is the material’s yield strength, t is the wall thickness, and D is the outer diameter. A safety factor of between 3:1 and 4:1 is typically applied.

6. Guide to Selecting Steel by Application

Application AreaPiston Rod SteelCylinder TubeSpecial Requirement
Construction machinery (excavator, loader)42CrMo4 + chromeST52 honed tubeHigh impact resistance, heavy load
Industrial press systems42CrMo4 + induction + chromeST52 thick wallHigh pressure (350–700 bar)
Agricultural equipmentC45 + chromeST52 standardCost optimization
Marine and offshoreAISI 316 or Ni+Cr coated C45Stainless / special alloyHigh corrosion resistance
Food and pharmaceutical industryAISI 316Stainless steel tubeHygiene, FDA compliance
Mobile hydraulics (crane, tipper)20MnV6 + chromeST52 honed tubeWeldability, lightweight

7. Critical Factors to Consider When Selecting Steel

  • Operating pressure: While C45 is generally sufficient for pressures below 250 bar, 42CrMo4 should be preferred for pressures between 250 and 700 bar. Applications exceeding 700 bar require special design and materials.
  • Environmental conditions: In environments containing saltwater, chemicals, or high humidity, standard chrome plating may not be sufficient. A dual-layer (nickel + chromium) coating or stainless steel may be required.
  • Stroke length: For long-stroke cylinders (over 1.5 meters), the straightness of the piston rod and its resistance to bending are critical. Higher-strength steel (42CrMo4) or thicker cross-sections may be required.
  • Operating temperature: In high-temperature applications (especially above 150°C), changes in the steel’s mechanical properties and the chrome plating’s thermal shock resistance must be considered.
  • Seal compatibility: The surface roughness of the piston rod must be suitable for the type of seal used. Extremely smooth surfaces may fail to lubricate the seal, while excessively rough surfaces can cause premature wear. A Ra value of 0.1–0.4 µm is generally ideal.

8. Evaluation Criteria in the Procurement Process

Hydraulic cylinder manufacturers should evaluate the following criteria when selecting steel bar suppliers:

Material certificate (EN 10204 Type 3.1): A complete certificate containing the casting number, chemical analysis, mechanical test results, and dimensional measurements is mandatory, particularly for export and OEM projects.
Tolerance class guarantee: h8 or h9 tolerances on piston rod bars reduce the need for grinding prior to chrome plating, thereby lowering labor costs.
Straightness and ovality control: For long piston rods, straightness deviation must not exceed 0.5 mm/m, and the ovality difference must not exceed half of the tolerance band.
Stock width and length cutting: Maintaining stock across a wide diameter range (20–200 mm) and offering custom length cutting services ensures production continuity.
Multi-location advantage: Suppliers capable of fast delivery from multiple locations provide a logistical advantage for urgent orders.

8.5. Future Trends in Hydraulic Cylinder Steel

The hydraulic cylinder industry is undergoing significant transformations driven by sustainability demands and technological innovations. These changes are directly impacting the selection of steel bars and supply strategies.

Environmental regulations are also affecting the chrome plating process. EU REACH restrictions on the use of hexavalent chromium (Cr6+) are driving the industry toward trivalent chromium (Cr3+) processes and alternative surface coating technologies. Laser cladding, HVOF (High-Velocity Oxy-Fuel) thermal spray, and ceramic coatings are emerging as technologies that will compete with chrome plating in the future. These new coating methods may impose different requirements on the surface properties of the underlying steel bar material.

The rise of micro-alloyed steels is also a notable trend. Vanadium-micro-alloyed grades such as 20MnV6 reduce energy consumption and the carbon footprint by eliminating heat treatment costs. With the introduction of the CBAM (Carbon Border Adjustment Mechanism) regulation in Europe, the supply of steel with a low carbon footprint is becoming a competitive advantage for hydraulic cylinder manufacturers.

Additionally, the growing prevalence of electrohydraulic actuators and compact cylinder designs is increasing demand for higher-strength steels. Cylinders capable of producing the same force in smaller cross-sections require steel bars with higher yield strength. This trend will increase the usage of high-alloy steels such as 42CrMo4 and 34CrNiMo6.

Digitalization is also transforming the supply process. Hydraulic cylinder manufacturers are beginning to expect digital material certificates, real-time inventory information, and the electronic sharing of quality data from steel suppliers. Industry 4.0 integration will improve quality management processes by increasing transparency and traceability in the supply chain.

.

Automotive Supplier Industry: Gear shafts (42CrMo4), synchronizer rings (16MnCr5), hydraulic fittings (11SMn30)
Hydraulics and Pneumatics: Piston shafts (42CrMo4 or C45, chrome-plated), valve bodies (11SMn30), cylinder heads (S355JR)
General Machinery Manufacturing: Bearing seats (C45), coupling parts (42CrMo4), pulleys (S355JR)
Defense Industry: High-strength shafts and axle components (34CrNiMo6), gearbox components (20MnCr5)
Energy Sector: Turbine shafts (42CrMo4), flange components (S355JR), wind turbine components (34CrNiMo6)

Material certificate (EN 10204 Type 3.1): CNC machining companies require a Type 3.1 certificate for material traceability, particularly in automotive and aerospace projects. Ensure that your supplier can provide this document.
Dimensional accuracy: Check the tolerance class of cold-drawn bars. Tolerances such as h9, h10, or h11 determine the preparation requirements before CNC machining.
Straightness and ovality: Warping and ovality in bar stock can cause issues during clamping on the CNC machine. Request a straightness guarantee from your supplier.
Stock variety: A supplier offering a wide range of sizes in round, square, flat, and hexagonal profiles can serve as a single-source provider for your various CNC projects.
Cutting service: Suppliers offering length-cutting services can shorten your CNC preparation process and reduce material waste.

Frequently Asked Questions (FAQ)

What type of steel is most commonly used for the piston rod of a hydraulic cylinder?

The most commonly used grade worldwide is C45 (CK45). It is available in cold-drawn, annealed, and hard-chromium-plated forms. For high-pressure or heavy-duty applications, 42CrMo4 is preferred.

What should the thickness of the chrome plating be?

For standard industrial applications, a chrome plating thickness of 20–25 micrometers is recommended, while for harsh conditions (mining, marine), a thickness of 40–50 micrometers is recommended. As plating thickness increases, corrosion and wear resistance improve, but so does the cost.

Can I use hot-rolled bars instead of cold-drawn bars?

It is technically possible but not recommended. Hot-rolled bars require more grinding due to their wider tolerances and their rough surface necessitates an additional preparation process prior to chrome plating. Cold-drawn bars typically reduce the total production cost of piston rods by 15–20 percent.

When should a stainless steel piston rod be used?

Stainless steel (AISI 316) is preferred in highly corrosive environments such as marine, food processing, pharmaceutical manufacturing, and chemical processing, as well as in applications with stringent hygiene requirements. For standard industrial applications, chrome-plated C45 or 42CrMo4 offers a much more economical solution than stainless steel.

Conclusion: Steel Bars Used in Hydraulic Cylinder Manufacturing and Selection Criteria

The selection of steel bars in hydraulic cylinder production is a strategic decision that determines the cylinder’s performance, service life, and total cost. For the piston rod, C45 offers ideal solutions for standard applications, 42CrMo4 for high-performance requirements, and 20MnV6 for cost-effective modern designs.

To make the right choice, comprehensively evaluate the operating pressure, environmental conditions, stroke length, and chrome plating requirements. By opting for cold-drawn steel bars, you can both enhance chrome plating quality and reduce your total production costs.

 

As Uyar Çelik, we supply cold-drawn round steel bars in grades such as C45, 42CrMo4, 20MnV6, and other high-quality steels to hydraulic cylinder manufacturers.

Contact us for the supply of Type 3.1 certified, tight-tolerance bars from our locations in Istanbul, Karabük, Kocaeli, and Düsseldorf.

  www.uyarcelik.com/iletisim

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Guide to Mold Steel: The Right Material for Plastic Injection and Hot Forging Molds

Guide to Mold Steel: The Right Material for Plastic Injection and Hot Forging Molds

Tabii, senin verdiğin kelimeyi paragrafa doğal şekilde eklenmiş hali burada:

The selection of mold steel is one of the most critical decisions determining a mold’s service life, production quality, and total cost. For Plastic Injection and Hot Forging Molds, the required performance criteria can differ significantly. While surface quality, dimensional stability, and corrosion resistance are paramount in plastic injection molds, high-temperature resistance, thermal fatigue resistance, and toughness are the key factors in hot forging molds.

Incorrect steel selection leads to premature mold failure, high maintenance costs, reduced product quality, and production downtime. The right choice, however, extends mold life, reduces maintenance frequency, and lowers the cost per part.

In this guide, we provide a detailed overview of the steel grades used in Plastic Injection and Hot Forging Molds, along with selection criteria, heat treatment requirements, and application recommendations.

1. What Is Die Steel and Why Is It Important?

Die steels are a specialized subcategory of tool steels used in the forming processes of metal or plastic materials. Possessing properties such as high wear resistance, thermal fatigue resistance, hardness, and toughness, these steels differ fundamentally from general-purpose structural steels.

Die steels are classified into two main categories: cold-work tool steels (typically used in dies operating below 200°C) and hot-work tool steels (used in dies operating above 200°C, particularly in the 300–1200°C range). While plastic injection molds are generally classified under the cold work category, hot forging dies fall under the hot work category. In both categories, the raw steel material—whether round, square, or flat steel bars—is machined using CNC in mold manufacturing facilities to achieve the final mold shape.

2. Selection of Steel for Plastic Injection Molds

A plastic injection mold is a precision tool into which molten plastic is injected under high pressure, cooled to solidify, and shaped into the desired form. The key properties expected from mold steel are as follows:

Good machinability: It must be easily machinable using CNC milling and electrical discharge machining (EDM).
Polishability: It must be capable of achieving a mirror finish (SPI A-1) for products requiring transparent or glossy surfaces.
Dimensional stability: It must exhibit minimal distortion after heat treatment.
Corrosion resistance: Stainless steel grades are required for plastics that produce corrosive gases, such as PVC and ABS.
Wear resistance: High hardness is essential to resist surface wear in glass-fiber-reinforced plastics.

Steel GradeDIN EquivalentHardness (HRC)TypePolishabilityTypical Application
1.273840CrMnNiMo8-6-128–32Pre-hardenedGoodLarge injection molds, automotive parts
1.231240CrMnMoS8-628–32Pre-hardenedMediumMold bases, holder plates, high machinability
1.2344X40CrMoV5-148–52Requires hardeningGoodHot runner components, high-temperature applications
1.2083X42Cr1348–52Requires hardeningExcellentCorrosive plastics (PVC), transparent products, medical applications
1.2316X38CrMo1628–32Pre-hardenedExcellentPre-hardened applications requiring corrosion resistance
1.1730C45UNormalizedBasicLowMold frames, support plates, prototype molds

2.1. Pre-hardened Die Steels (1.2738, 1.2312)

Pre-hardened die steels are supplied by the manufacturer with a hardness range of 28–32 HRC and can be machined directly on CNC machines without requiring additional heat treatment. This significantly reduces die manufacturing time and eliminates the risk of heat treatment distortion.

1.2738 is the most widely preferred grade worldwide for large-scale injection molds. Thanks to its nickel alloy composition, it ensures a homogeneous hardness distribution even in large cross-sections. 1.2312, on the other hand, features enhanced machinability due to its sulfur content and offers a cost advantage in applications where polishability is not critical, such as mold bases and retaining plates.

2.2. Sertleştirilebilir Kalıp Çelikleri (1.2344, 1.2083)

Yüksek aşınma direnci veya korozyon direnci gerektiren uygulamalarda sertleştirilmiş kalıp çelikleri tercih edilir. Bu çelikler CNC ile yarı finisaj işlemesinden sonra ısıl işleme tabi tutulur ve 48–52 HRC sertliğe ulaşır.

1.2083 (X42Cr13), yüksek krom içeriği (çoğunlukla yüzde 13 Cr) sayesinde paslanmaz özellik gösterir. PVC, asetal ve alev geciktirici katkılı plastiklerin kalıplanmasında korozyon direnci sağlar. Aynı zamanda mükemmel cilalanabilirliği ile şeffaf optik parçalar ve medikal bileşenler için idealdir.

3. Selection of Steel for Hot Forging Dies

Hot forging dies are used to shape metal parts heated to temperatures between 900–1250°C under high pressure. These extreme conditions demand very different properties from the die steel:

High-temperature hardness retention: The die surface is continuously exposed to temperatures of 500–600°C and must retain its hardness.
Resistance to thermal fatigue: The rapid heating-cooling cycle during each forging cycle can cause thermal cracking (heat checking) on the surface. The steel must be resistant to this.
Toughness: The ability to deform without fracturing under forging impacts is of critical importance.
Wear resistance: Metal flow at high temperatures wears down the die surface; the steel must be resistant to this.

Steel GradeDIN EquivalentHardness (HRC)Max Operating Temp.Typical Application
1.2344X40CrMoV5-1 (H13)44–52~600°CGeneral forging dies, Al/Cu extrusion, die casting
1.2343X38CrMoV5-144–50~550°CForging and drawing dies requiring higher toughness
1.271456NiCrMoV740–48~500°CHeavy forging dies, hammer dies, high-impact applications
1.2367X38CrMoV5-344–52~650°CSuperior thermal fatigue resistance, high-performance applications

4. The Relationship Between Heat Treatment and Steel Quality

The performance of die steels depends on the application of proper heat treatment. Pre-hardened steels (1.2738, 1.2312) are delivered with a pre-set hardness value and therefore do not require additional heat treatment. However, hardenable steels (1.2344, 1.2083, 1.2714) must undergo controlled quenching and tempering.

Heat treatment is particularly critical for hot-forging die steels. For example, to achieve optimal performance with 1.2344, austenitization at 1020–1040°C, followed by oil or air cooling and then two tempering cycles, is typically applied. The tempering temperature is selected between 520–620°C depending on the desired balance of hardness and toughness.

Important note: Dimensional changes occurring during heat treatment are directly related to CNC machining. The general approach for heat-treating die steels is: rough machining → heat treatment → finish machining.

5. Die Steel Raw Material Forms: Bar, Block, and Plate

Die steels are available in various raw material forms. Selecting the correct form directly impacts die manufacturing efficiency:

Round steel bar: Ideal for cylindrical die components (rollers, nozzles, injector bodies). It offers tight tolerances and a smooth surface when supplied in cold-drawn form.
Square steel bar: Used as raw material for small and medium-sized mold inserts, cores, and rollers. Provides a holding advantage for CNC milling.
Steel blocks and plates: Used for large mold bases and cavity blocks. Typically supplied in hot-rolled or forged form.
Steel plates: Suitable for mold guide elements, scraper plates, and support components.

6. Sectoral Differences in Selection Criteria

6.1. Automotive Industry

Automotive plastic parts are typically produced in high volumes (hundreds of thousands or even millions of units). For this reason, 1.2738 is preferred as mold steel, and 1.2344 is preferred for glass-fiber-reinforced plastics. In hot forging, 1.2714 and 1.2344 are commonly used for forging critical automotive components such as crankshafts, connecting rods, and gears.

6.2. Medical and Food Industry

Due to hygiene requirements, corrosion resistance is a top priority. Stainless steel grades such as 1.2083 or 1.2316 are preferred. High polishability reduces bacterial adhesion and facilitates cleaning.

6.3. Home Appliances and Consumer Products

Surface finish quality is critical. While 1.2738 pre-hardened die steel is the standard choice, 1.2083 stands out for its mirror-finish capability in transparent parts.

7. Common Mistakes and Recommendations

  • Over-engineering: Using high-alloy steel for prototypes or low-volume dies creates unnecessary costs. 1.1730 (C45U) may be sufficient in this case.
    Incorrect heat treatment: Even high-quality steel loses its performance with improper heat treatment. The correct tempering temperature and duration are particularly critical for hot forging dies.
  • Ignoring corrosion risk: Using standard steel when processing PVC and flame-retardant plastics leads to premature corrosion on the die surface.
    Compromising on raw material quality: The distribution of inclusions and homogeneity in die steel directly affect polishability and die life. Low-quality raw material is cheap in the short term but expensive in the long term.

Future Trends in Die Steel and Surface Treatments

The die steel industry is constantly evolving in response to industrial demands and technological innovations. Certain trends that have emerged in recent years, in particular, are directly influencing steel selection and die design.

Surface treatments and coatings are critical technologies that extend die life. The nitriding process significantly increases wear resistance by forming a thin nitride layer on the die surface with a hardness of 800–1200 HV. PVD (Physical Vapor Deposition) coatings, particularly TiN, TiAlN, and CrN coatings, reduce sticking in plastic injection molds and protect the die surface. In hot forging dies, nitriding is the most common surface treatment and can extend die life by 30–50 percent.

Conformal cooling channels are cooling channels produced using 3D metal printing technology that follow the part’s geometry within the die, unlike traditional straight holes. This technology can reduce cycle time by 20–40% and minimize warping and distortion defects. Conformal cooling inserts are typically 3D-printed from maraging steel or special alloys like 1.2709 and integrated into the traditional die steel body.

Powder metallurgy (PM) mold steels are another emerging technology. Steels produced via the PM method offer a much more homogeneous carbide distribution compared to traditional cast steels. This provides significant advantages, particularly in optical and medical applications that require high polishability and long mold life.

From a sustainability perspective, die steels have a high recyclability rate. Dies that have reached the end of their service life are classified as scrap and returned to the steel production cycle. With the introduction of European CBAM regulations, the supply of steel with a low carbon footprint is becoming an increasingly important criterion for supplier selection in the die industry as well.

On the supply side, the trend toward digitalization is gaining momentum. Die manufacturers have begun expecting digital material certificates, real-time inventory information, and rapid cutting services from steel suppliers. Suppliers capable of delivering quickly from multiple locations and maintaining inventory across a wide range of diameters and profiles are gaining a competitive advantage.

Frequently Asked Questions (FAQ)

What type of steel is most commonly used for plastic injection molds?

1.2738 (pre-hardened, 28–32 HRC) is the most widely used plastic injection mold steel worldwide. It can be machined directly without requiring additional heat treatment, provides uniform hardness across large cross-sections, and offers good polishability. For corrosive plastics, 1.2083 or 1.2316 is preferred.

What type of steel is used to make hot-forging dies?

1.2344 (H13) is the most commonly used grade for hot-forging dies. It offers hardness retention at high temperatures and resistance to thermal fatigue. For hammer forging, where heavy impact loads are present, 1.2714 is preferred due to its higher toughness.

What is the difference between pre-hardened and hardened die steel?

Pre-hardened steels (1.2738, 1.2312) are supplied with a ready-to-use hardness value (28–32 HRC) and require no additional heat treatment; the mold manufacturing time is short. Hardened steels (1.2344, 1.2083), on the other hand, are heat-treated after machining to achieve a hardness of 48–52 HRC; they offer higher wear resistance but have a longer production cycle.

In what form should I purchase the raw material for die steel?

Cold-drawn round bars are preferred for cylindrical mold components, square bars for small-to-medium inserts, and blocks or plates for large cavity blocks. Cold-drawn bars reduce CNC machining costs thanks to their tight tolerances and good surface quality.

The delivery condition of the steel bar is also important when selecting the raw material form. Cold-drawn bars can be delivered in annealed or normalized condition. In pre-hardened mold steels (1.2738, 1.2312), the bar is already delivered at a hardness of 28–32 HRC, making it ready for direct CNC machining. For grades that require hardening, the bar is received in a normalized or annealed condition, undergoes rough machining first, and then undergoes heat treatment. This sequence is critical for efficiency and dimensional accuracy in die manufacturing. Having your supplier stock different delivery conditions provides flexibility for your die projects.

Conclusion: Die Steel Guide: The Right Material for Plastic Injection and Hot Forging Dies

The selection of mold steel should be based on the type of mold (plastic injection or hot forging), production volume, the properties of the material to be processed, and the expected mold life. In plastic injection molding, 1.2738 and 1.2083 are prominent industry standards, while in hot forging, 1.2344 and 1.2714 are the leading choices.

When the right steel material is combined with the correct heat treatment and the appropriate die design, die life is extended, maintenance costs are reduced, and the production cost per part is optimized.

As Uyar Çelik, we supply cold-drawn round, square, and flat steel bars in grades 1.2344, 1.2738, 1.2714, C45, and other high-quality steel grades to die-casting foundries.

For the supply of Type 3.1 certified, tight-tolerance bars from our locations in Istanbul, Karabük, Kocaeli, and Düsseldorf: 

www.uyarcelik.com

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